In Weka 3.8.3 get different result when set the probaabilityEstimates true or false - svm

Question

I use the same training data set and testing data set.
And I choose Weka classifiers-> functions-> LibSVM , and use default parameters.
I use default parameter and get the result:
https://imgur.com/aIq90wP
When I set the parameter probabilityEstimates to true, I get this result:
https://imgur.com/NGVY5No
The default parameters set are like this:
https://imgur.com/GOfLnVd
Why am I getting different results?
Maybe it's a silly question but I'll be grateful if someone can answer this.
Thanks!

Answer 1

This seems to be related to the random number process.
I used the same libSVM, all defaults, with diabetes.arff (comes with the software).
Run 1: no probabilityEstimates, 500 correct
Run 2: same, 500 correct
Run 3: probabilityEstimates, 498 correct
Run 4: same, 498 correct (so, with identical parameters, the process replicates)
Run 5: probabilityEstimates, but change seed from 1 to 55, 500 correct.
Run 6: probabilityEstimates, but change seed from 55 to 666, 498 correct.
Run 7: probabilityEstimates, but change seed from 666 to 1492, 499 correct.
The algorithm needs, for whatever reason, a different amount of random numbers or uses them in a different order, resulting in slight perturbations in the number correct when probabilityEstimates are requested. We get the same effect if we change the random number seed (which tells the random number generator where to start).