sluggish mouse movement
as you said... you already know this
I've noticed this yesterday. I generally use a mouse with a high polling rate, but replacing it with a very cheap mouse with a low polling rate 'solves' this problem. Maybe that'st the direction you should look for.
xD
Thanks for the hint! This will be a little hard to test, but it sounds like a probable cause.
I do manual mouse polling through Allegro 4 in the game to implement hold-RMB-scrolling, so my mouse code is nonstandard in this regard. The game logic, including the polling, runs at 60 or 120 Hz, usually at 60.
In March 2015, I have begun a full rewrite of the game in D using Allegro 5. Mouse problems are practically gone there. As of October 2015, the D port is far from finished; it demonstrates the fundamental graphics classes.
The C++/Allegro 4 codebase will continue to get critical updates until the D port is finished. However, I won't work on the mouse code in the C++/Allegro 4 version myself. If someone would like to send in a patch, that patch can still get merged.