In my application we use AvalonDock for a docking manager, and have a variety of different windows. One of those contains an AvalonEdit editor. We recently noticed one specific interaction issue which I figured out to be caused by the AvalonDock.
When trying to block select code, you can use a bunch of different methods: Alt + click and drag, Alt + Shift + click and drag, Alt + Shift + arrow keys, and so on. One specific method, Alt + click and drag doesn't work. Specifically it does select, but typing doesn't work until you press either escape or space once. With Alt + Shift + click and drag it works fine.
I tested the AvalonEdit sample project as well as making my own simple example and it worked fine. When I put a test AvalonEdit window in a Window control instead of within a UserControl that's docked in my docking manager, it works fine. So something is going on with the interaction between having the AvalonEdit window within a AvalonDock vs. having it within some other window. Has anyone worked with these two controls together before? I know they're both used in SharpDevelop so I'd expect that they should work well together.
I found another issue which also has an alt-related issue with AvalonDock but it doesn't seem to be exactly what I'm seeing: AvalonDock Now Loses Alt Key Adornments. Also they claim that issue has been fixed, and I can't even test the solution in the answer as I don't have/use Blend. Looking at that bug makes me think it's more an issue with AvalonDock though and not AvalonEdit
In the end it turned out that
AvalonDockwasn't the culprit directly. The real issue was a WPF Ribbon control which was stealing the focus when you pressed Alt. Killing hotkeys on the Ribbon fixed the editor interactions.