incrementation occurs two times in a groovy script within soapui

Hello I'm trying to do a simple groovy script in Soapui

I try to get a testcase property and increment it then save it. when I run then script it increments it two times I don't know why. I tried different syntaxes but nothing seems to work up to now.

Here is a screenshot that shows my problem

here I run the test 2 times, first the variable was 3, normally when I run the test the second time the before value should be at 4 and the after at 5, and not 5 and 6.