I'm just collecting all of the posts on this issue here because I have yet to find a working solution. Maybe by having them all accessible from one location, I might be able to synthesize an answer somehow.

The issue is that the map will scroll after about six to eight seconds. Re-centering the map on the characters does not resolve this issue. The issue occurs with a fresh install when installed to root, when installed to my documents, when installed to program files x86. Widescreen mods do not correct this issue. I am running the game on a laptop with a touchpad and do not have any external mice and do not have logitech drivers. Based on the descriptions other people shared, I do not believe that the issue is related to a specific mouse-type. Scroll lock and shift lock are not enabled. I am running windows 7 64-bit, although it appears that this issue has been spotted on windows xp as well. I do not believe it to be OS-specific either.

I haven't fully ruled out anything but I also do not know where to start. I will start by gathering as much info as I can:

Workaround?
http://www.gog.com/forum/planescape_torment/camera_issues
"The only way I can fix this is fixating the camera on The Nameless One."

Issue with different symptoms with dead links to bioware forums:
http://www.gog.com/forum/planescape_torment/no_reply_to_topic_trying_again_please_help
"There have been problems over the years with IE games (BG / BG2 / IWD / IWD2 / PS:T) and various cordless meece/keyboards . "

Unresolved issue from 2010:
http://www.gog.com/forum/planescape_torment/map_goes_crazy_randomly
"For the past few days, any time I try to scroll around the local map, the arrow drags me to the top left corner of the map and stays there until I force it down to wherever my team is... ...This happens over and over until I get so frustrated, I give up and quit. "

Unresolved:
http://www.gog.com/forum/planescape_torment/mouse_scrolling_issueplease_help

Hopefully I will find a solution, but I might not be able to as there is very limited data available.

I am also experiencing the same issue but can't seem to find a proper fix. I have found that entering the options menu and exiting it fixes the issue for a while until you have to do it again.

I've had this happen a few times in all time I've worked with PST but I could never reliably reproduce it. Rebooting usually fixed it so I always thought it might be some system glitch with IE/PST. It's also not a very easy issue to pin point since I could never figure out what the trigger was.

This exact problem is happening for me as well. I have all the same specs as the OP except I am using a wireless mouse. I have not attempted to install any widescreen mods.

Having this issue on a fresh install of the game. It didn't happen until I had closed the game for the first time and loaded a save. I'm on a Razer Diamondback (not cordless) on Windows 7 64-bit. No mods used. Rebooting the game or Windows does not help. Only way to solve this is to center the camera on the Nameless One, but unfortunately this makes moving extremely slow since you need to keep clicking all the time.

I'm on a dualscreen setup, so this may be related to the issue.