This forum is actively monitored by JRiver staff, including the lead developer (Matt) and the CEO (JimH). I just don't happen to work for them (though I'm an admin on the forum, I just help with thread management tasks and spam and stuff).
I'm sure someone will respond. However, I'd be willing to bet from experience that the answer I gave is the answer.
I'd recommend that you attempt to solve your issue. If it is a bug in MC (and if it worked and still works with MC19 on your Windows install, and works on the OSX version, then it would seem likely that something odd is going on anyway), they'll try to investigate and fix it. But it didn't look like you were looking for that kind of help.