Weird behaviour of a counter in process() method of Javacard - javacard

Question

I use a static short field named counter in the process() method of my Java Card applet to count the number of this method firings!
Well, the program is really simple and looks like this:
package testPack;
import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISOException;
public class Test extends Applet {
public static short counter = 0x0000;
public static void install(byte[] bArray, short bOffset, byte bLength) {
new Test().register(bArray, (short) (bOffset + 1), bArray[bOffset]);
}
public void process(APDU apdu) {
if (selectingApplet()) {
return;
}
counter = (short) (counter + 1);
ISOException.throwIt(counter);
}
}
When I install this applet in the regular way, it works fine:
Regular Installing:
GlobalPlatformPro:> gp -list
AID: A000000151000000 (|....Q...|)
ISD OP_READY: Security Domain, Card lock, Card terminate, Default selected,
AID: A0000001515350 (|....QSP|)
ExM LOADED: (none)
A000000151535041 (|....QSPA|)
GlobalPlatformPro:> gp -install d:\test.cap
GlobalPlatformPro:> gp -list
AID: A000000151000000 (|....Q...|)
ISD OP_READY: Security Domain, Card lock, Card terminate, Default selected,
AID: 010203040501020304 (|.........|)
App SELECTABLE: (none)
AID: A0000001515350 (|....QSP|)
ExM LOADED: (none)
A000000151535041 (|....QSPA|)
AID: 010203040501 (|......|)
ExM LOADED: (none)
010203040501020304 (|.........|)
Regular installing, applet output:
OpenSCTool:> OSC.exe -s 00A4040009010203040501020304 -s 00000000
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 09 01 02 03 04 05 01 02 03 04
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x01)
OpenSCTool:> OSC.exe -s 00A4040009010203040501020304 -s 00000000 -s 0000000
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 09 01 02 03 04 05 01 02 03 04
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x02)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x03)
But when I install it as default selected applet, the counter works different:
installing as Default selected applet:
GlobalPlatformPro:> gp -list
AID: A000000151000000 (|....Q...|)
ISD OP_READY: Security Domain, Card lock, Card terminate, Default selected,
AID: A0000001515350 (|....QSP|)
ExM LOADED: (none)
A000000151535041 (|....QSPA|)
GlobalPlatformPro:> gp -install d:\test.cap -default
GlobalPlatformPro:> gp -list
AID: A000000151000000 (|....Q...|)
ISD OP_READY: Security Domain, Card lock, Card terminate, CVM (PIN) managem
AID: 010203040501020304 (|.........|)
App SELECTABLE: Default selected
AID: A0000001515350 (|....QSP|)
ExM LOADED: (none)
A000000151535041 (|....QSPA|)
AID: 010203040501 (|......|)
ExM LOADED: (none)
010203040501020304 (|.........|)
Default selected, applet output:
OpenSCTool:> OSC.exe -s 00A4040009010203040501020304 -s 00000000
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 09 01 02 03 04 05 01 02 03 04
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x06)
OpenSCTool:> OSC.exe -s 00A4040009010203040501020304 -s 00000000 -s 0000000
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 09 01 02 03 04 05 01 02 03 04
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x0C)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x0D)
As you see above, when I installed the applet as Default Selected, the counters increases by 6 with each command (instead of increasing by 1)!
What is happening on the background?
Update 1:
Based on dear #Vojta's comment, I changed the program in way to increase the counter value for APDU commands with CLA = 0x80 only:
public void process(APDU apdu) {
if (selectingApplet()) {
return;
}
byte[] buffer = apdu.getBuffer();
if ((buffer[ISO7816.CLA_ISO7816] & 0x00FF) == 0x80 ) {
counter = (short) (counter + 1);
}
ISOException.throwIt(counter);
}
This is the output (for Default selected case):
OpenSCTool:> OSC.exe -s 00A4040009010203040501020304 -s 00000000 -s 8000000
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 09 01 02 03 04 05 01 02 03 04
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x00)
Sending: 80 00 00 00
Received (SW1=0x00, SW2=0x01)
OpenSCTool:> OSC.exe -s 00A4040009010203040501020304 -s 00000000 -s 80000000
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 09 01 02 03 04 05 01 02 03 04
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x01)
Sending: 80 00 00 00
Received (SW1=0x00, SW2=0x02)
OpenSCTool:> OSC.exe -s 00A4040009010203040501020304 -s 00000000 -s 8000000
Using reader with a card: ACS CCID USB Reader 0
Sending: 00 A4 04 00 09 01 02 03 04 05 01 02 03 04
Received (SW1=0x90, SW2=0x00)
Sending: 00 00 00 00
Received (SW1=0x00, SW2=0x02)
Sending: 80 00 00 00
Received (SW1=0x00, SW2=0x03)