Fullscreen problem on High Sierra

When recently testing fullscreen on High Sierra I found another issue. From the main window of my app a Setup window can be opened. This has an ugly black frame around it:

When clicking on another item on the toolbar the window only shows the toolbar but not the window part. The window has fullscreen off but resizable on. If I set resizable to off the odd effect goes away. Unfortunately, I can’t reproduce this in a simple example. Has anyone else seen this?

Do you have maxwidth and max height set smaller than your screen?

Also, check the states of the maximize button. I seem to remember that it needs to be on for full screen to work properly.

Both Maximise and Fullsize button were set to off. But as soon as I set Resizable to true those settings don’t seem to matter anymore on High Sierra. MaxWidth and MaxHeight were set to 1000. The screen of the MacBook Air is 1440x900 so I changed the MaxHeight to 800. But this didn’t make a difference.

What is also a useability problem is that the window should have 2 different sizes for different selections of toolbar. When the black frame is visible the size of the window doesn’t change.

Try setting max height and maxwidth to something larger than your screen and see if that fixes the sizing issue.

Nope, no change. For now I’ll disable Resizable.