Hi Brett,
This is something we are aware of and has been a particularly frustrating issue. There is a description of our findings in this thread:
The summary is that we have to handle WM_GETMINMAXSIZE so that we don't cover up an auto-hidden taskbar. But then if we handle that WM_GETMINMAXSIZE message, it introduces this issue you see. We were able to reproduce it in a simple project that doesn't even use our controls, simply by handing that message. So far we haven't found a workaround short of not handling WM_GETMINMAXSIZE.
But this did give us an idea that were just tried. We updated our WM_GETMINMAXSIZE handler to effectively not do anything if it detects the taskbar is not auto-hidden. This fixes the issue you reported in scenarios where the taskbar is not auto-hidden, which is most common. If you would like to help test this update, please write our support address and reference this post.