After I insatlled BG2 Fixpack and BG 2 Tweakpack, I noticed boots of speed no longer work as they should - they haste the character speed, but not their attack speed. Besides, I noticed that the character wearing boots of speed walk like BG1, not like BG2. I thought I had mistakenly installed the "Use BG1 Walking Speed" mod, but I checked it again confirmed that I hadn't.
Now, what really annoys me is that, although I have uninstalled both mods, the boots of speed still do not work as they should - and, yes, I tested it in a new game.
I also have the Dungeons Be Gone mod installed, but I find it unlikely that it would mess boots of speed.