Counters for one side show the masked image when hidden and you mouse over the other shows the counter without being masked why?

This has been fixed in the Vassal 3.7.22 Release. Give that a try. If it still doesn’t work consider opening an issue like the one above.

Please consider to check the solution to your problem - only you as OP can do that. That helps others find a possible solution to their problems.

Yours,
Christian