I've got  a 720 with GPS version 7.5.19 and OS 1.0.1.16.
1.  Today, I used the calculator for the first time to add up my recent flight hours.  Every time I entered the 4th or 5th integer (or decimal  number) in a series, the calculator screen would go hinky, displaying 7,2/12 (or some such) as the current sum.  YES, it would display a comma and a backslash....diffterent numbers each time but not germane to the sum of my entries.  This would happen before I clicked the = sign.  When I contiued, the final sum was a similar, meaningless display.  I've tried this about a dozen times with the same result (both with the GPS running in the background and not).   The calculator  is not functional or reliable.
2.  Every time I post on this forum and click spell check...my screen locks up and I have to restart IE....Could be me...I'm using IE 9 with Windows 7.  Has anyone else had this problem?
Have no doubt, I LOVE this GPS.
~Gerry