As the title says it happens systematically (any time I insert a new variation or perform other "basic" operations in Scid) that:
The problem is solved by selecting any other opened window (e.g. browser) and by selecting Scid again. If Scid is the only active window M-TAB solves the problem.
In ScidVsPC a similar problem occurred to me with some older versions and it was sometimes solved by clicking repeatedly on the Notation/Comment Editor window. In Scid this doesn't happen.
I'm using Version 4.7.4 of Scid on Ubuntu 22.04.
Using v5.0.2 the steps to reproduce are:
It looks like the arrow key + Ctrl-a work only as long as the Notation window has the focus. To my mind, the board should respond to those key strokes the same way that Notation window does.
If you could give me a hint where to look in the code base, I can give it a shot and see if I can fix it 🤞