Please check out r21256, it should hopefully resolve all remaining focus issues with the editor windows.

The above issues are fixed, but there's a new and quite strange one.
When switching from an OPL instrument to a normal sample the focus doesn't go to the sample view but instead gets stuck. Afterwards it remains stuck even when switching back to the previous OPL instrument. The only way to make it behave well again is to switch tabs. Also, when the sample editor is in this inconsistent state, it's not possible to return to it from the instrument library by pressing Alt+S, the shortcut simply does nothing.

Please check r21267.

Unfortunately r21267 makes no difference in this case. After switching from an OPL instrument to a normal sample via prev/next shortcuts the focus becomes trapped in the already dead OPL control that was focused before the switch. Also, selecting a normal sample from the instrument library doesn't move the focus from the treeview at al.

This should now be fixed in r21281.

Switching samples with the treeview is now working properly, but the focus is still getting stuck in the OPL editor when using prev/next sample shortcuts. The following steps can be used to see this surprising thing in action:

1. Load or create a normal sample.
2. Initialize a new OPL instrument.
3. Focus the Modulation Feedback slider and leave it at 0%.
4. Press the Previous Sample shortcut, and then End.
5. Go back to the OPLL instrument. Modulation feedback will be at 100%.

So I guess the fix in 0001795 didn't work at all.

Yes, it seems so, although it did prevent tab navigation between hidden OPL controls.

One more try with r21285, please.

Now switching from an OPL instrument totally breaks keyboard input in the sample editor. All key presses just produce the default Windows dummy sound and do nothing else. Going to a different tab and back again helps to get out of this state.

r21288 should hopefully work better.

Wow! r21288 seems to have actually fixed this. Thank you!