Have you (or anyone who uses your PC) made any changes to the default mouse wheel scroll characteristics?
How many lines does a document scroll when you use the wheel?
The usual amount is 3, so if you scroll more than that someone has changed the wheel sensitivity - which would explain the problem in Shaiya.
Try clicking the Start button and then typing "mouse"
If you see a mouse configuration utility listed, have a look at that & see if you can modify that.
Let us know if this doesn't help & I'll try to think of something else
I don't recall seeing anywhere that you can change the mouse wheel sensitivity - but if it's anywhere in Shaiya it will be in the config.ini file.
Unfortunately I'm at work right now and can't check to see if there's anything there - I'll have a look when I get home in about 5 or 6 hours.