I was preparing screenshots to show you the difference between tooltips in BA versus tooltips in other programs in KDE5, but while I was doing that, I noticed that Gimp has the same issue of tooltips with white text on a gray background. Since most other programs have white on black tooltips, I realized that the problem is the way KDE5 (which is Qt5 based) renders Gtk programs. I went to KDE's Gtk settings and was able to solved the tooltip issue. I thought you'd like to know.
However, 18.104.22.168 still has issues with buttons (and other widget) not being large enough to display their captions. Here are a couple of examples:
Notice that the tabbed list on the left isn't wide enough to display the text of all the tabs. I wonder if it's possible for the widget's width to scale depending on the text instead of being fixed since available fonts will vary from system to system (and OS to OS). Also notice some of the buttons aren't wide enough for their text either.
Another example of button size issues: the "ACF", "VL" and "WL" buttons are clipping their text.
I'm not familiar with wxWidgets and their features, but hopefully you can figure out a solution that will make the widgets adaptable to the machine they are running on.
Keep up the good work!