No, this is definitely mangos bug that wasn't present in previous version.
I recently upgraded from
Server Version : 2118001
Database Version : Rel21.22.1
to
Server Version : 2201001
Database Version : Rel22.1.1
I have made no changes to the client like nampower so this has to be mangos related. The previous version worked fine.
I haven't checked all the spells but only some seem to have this issue. So far I noticed it with frostbolt and fireball.
Reproduce: cast frost bolt and keep pressing hotkey for another while it's casting... if you try to cast another spell right as the cast bar for the previous spell finishes, new cast bar appears red with the messege "failed" and an error message at the top says "another action is in progress".
I could make a video if that helps but I don't think you'll have any troubles reproducing this.