Invalid path errors with long URLs in Orchard CMS 1.9 - orchardcms

Question

Scenario: multitenant Orchard 1.9.3 deployment running in a single instance Azure Web App where all settings & media is stored in Azure blob storage.
After enabling File System Output Cache (so all cache items are stored in the App_Data\OutputCache folder, I see entries being added to the folder just fine. But it appears that items with long URLs are throwing errors and causing 500's to be thrown. Sometimes it's a long URL, but sometimes common campaign management links (UTM codes for Google Analytics) are causing issues to as they make long URLs too with the extra querystring options. The error, as you can see below, is Invalid Path when it tries to find the file in cache.
Here are a few of the errors (note the links in the errors work now as I've disabled cache and the errors have gone away).
I noticed there were changes to the File System Output Cache in the 1.9.x release... are long URLs an issue?
2016-05-09 00:00:17,596 [19] Orchard.OutputCache.Filters.OutputCacheFilter - Default - An unexpected error occured while reading a cache entry
http://www.andrewconnell.com/archive/2012/07/30/sharepoint-2010-metadata-based-navigation-in-publishing-sites-series-overview.aspx
System.ArgumentException: Invalid path
at Orchard.Validation.PathValidation.ValidatePath(String basePath, String mappedPath) in C:\Orchard\src\Orchard\Validation\PathValidation.cs:line 29
at Orchard.FileSystems.AppData.AppDataFolder.CombineToPhysicalPath(String[] paths) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 95
at Orchard.FileSystems.AppData.AppDataFolder.FileExists(String path) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 158
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.<>c__DisplayClass12_0.<GetCacheItem>b__0()
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.Retry[T](Func`1 action)
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.GetCacheItem(String key)
at Orchard.OutputCache.Filters.OutputCacheFilter.GetCacheItem(String key)
2016-05-09 00:00:17,628 [19] Orchard.OutputCache.Filters.OutputCacheFilter - Default - An unexpected error occured while reading a cache entry
http://www.andrewconnell.com/archive/2012/07/30/sharepoint-2010-metadata-based-navigation-in-publishing-sites-series-overview.aspx
System.ArgumentException: Invalid path
at Orchard.Validation.PathValidation.ValidatePath(String basePath, String mappedPath) in C:\Orchard\src\Orchard\Validation\PathValidation.cs:line 29
at Orchard.FileSystems.AppData.AppDataFolder.CombineToPhysicalPath(String[] paths) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 95
at Orchard.FileSystems.AppData.AppDataFolder.FileExists(String path) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 158
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.<>c__DisplayClass12_0.<GetCacheItem>b__0()
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.Retry[T](Func`1 action)
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.GetCacheItem(String key)
at Orchard.OutputCache.Filters.OutputCacheFilter.GetCacheItem(String key)
2016-05-09 00:00:32,565 [30] Orchard.OutputCache.Filters.OutputCacheFilter - mscloudshow - An unexpected error occured while reading a cache entry
http://www.microsoftcloudshow.com/blog/episode-087-catching-up-with-paul-schaeflein-on-azure-ad-improvements?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+MicrosoftCloudShow+(Microsoft+Cloud+Show)
System.ArgumentException: Invalid path
at Orchard.Validation.PathValidation.ValidatePath(String basePath, String mappedPath) in C:\Orchard\src\Orchard\Validation\PathValidation.cs:line 29
at Orchard.FileSystems.AppData.AppDataFolder.CombineToPhysicalPath(String[] paths) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 95
at Orchard.FileSystems.AppData.AppDataFolder.FileExists(String path) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 158
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.<>c__DisplayClass12_0.<GetCacheItem>b__0()
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.Retry[T](Func`1 action)
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.GetCacheItem(String key)
at Orchard.OutputCache.Filters.OutputCacheFilter.GetCacheItem(String key)
2016-05-09 00:00:32,581 [30] Orchard.OutputCache.Filters.OutputCacheFilter - mscloudshow - An unexpected error occured while reading a cache entry
http://www.microsoftcloudshow.com/blog/episode-087-catching-up-with-paul-schaeflein-on-azure-ad-improvements?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+MicrosoftCloudShow+(Microsoft+Cloud+Show)
System.ArgumentException: Invalid path
at Orchard.Validation.PathValidation.ValidatePath(String basePath, String mappedPath) in C:\Orchard\src\Orchard\Validation\PathValidation.cs:line 29
at Orchard.FileSystems.AppData.AppDataFolder.CombineToPhysicalPath(String[] paths) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 95
at Orchard.FileSystems.AppData.AppDataFolder.FileExists(String path) in C:\Orchard\src\Orchard\FileSystems\AppData\AppDataFolder.cs:line 158
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.<>c__DisplayClass12_0.<GetCacheItem>b__0()
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.Retry[T](Func`1 action)
at Orchard.OutputCache.Services.FileSystemOutputCacheStorageProvider.GetCacheItem(String key)
at Orchard.OutputCache.Filters.OutputCacheFilter.GetCacheItem(String key)