[Users] Select All shortcut Ctrl + A not working

[addicted2h]

4.0.0 is the last available version in the current Mint repository. I had previously used Claws 3.16 on a LM19.3 machine and didn't have any significant problems. 
After installing a new 21.1 Linux Mint, I installed Claws via the Software Manager. I added a few plugins, also via the Manager, and Clawsker again (mostly for "Display To column instead of From in Sent folder"). I've rebooted several times and done some minor cosmetic tweaking. Only after I had set everything up the way I wanted it did I fetch my new email from the server and noticed the odd problem: I no longer can use Ctrl + A as the shortcut to select all email messages in a folder in the message list view. I used to do that all the time, but now I have to go to the menu and pick the command. I checked via Clawsker, and re-did it, but the keyboard shortcut had already been correctly set to Ctrl + A. It is also not assigned to a different function on my system, as I use the same to select all in Nemo, the file manager. This is such an odd malfunction I don't even know where to start looking. Though I did search this list's archive, to no avail. Any ideas?