Please open a case with suppport.
This is actually as designed - please see KB67022 for details. (It's still relevant even though the article says MA 4.5 - I'll get that updated.)
Essentially what's happening is the task is actually configured to deploy the product in the branch that you choose: the interface tries to be helpful and shows you the build number, but if you then change the product version in that branch, you'll get this issue. I believe this may be addressed in MA 5: I'll test the current beta and update this thread.