The popup bubbles are tricky because we are converting from one resolution to the next. But I’m happy for you to dig around for a solution. Everything can be improved 
I haven’t merged the changes yet. But there is no hurry I suppose. I did update the JUCE source yesterday. It looks to have fixed all those file browser issues on Linux. I push it through the to dev branch. I’d be very happy to see the last of those issues!