Instability on iMac running Snow Leopard with Magic Mouse

I have problems at times selecting text with my Magic Mouse on my iMac running Snow Leopard. Often the source text jumps randomly when I click on a character in a line. This leads to problems with selecting text that I had no intention of selecting. I don't have this problem with other software.

Also I find it disconcerting that the cursor does not disappear when I begin to type text. This is a really easy fix.