Environment: Sonicwall TZ180 Firewall/Router (Wireless), Logitech MX Revolution (Wireless), NOD32 AV.
I've scoured the internet and found others having this same problem but no realistic solution. When you re-assign mouse buttons to perform functions requiring multiple keystrokes (IE, ALT + F4, etc.), it causes the left mouse button to bring up "properties" of an icon and almost complete screw-up possible selections on, for example, an open browser window. I located a good description of this problem as being "Stuck Key Modifiers," where the "ALT" remains engaged when the mouse button is clicked so any task after this button is used produces the wrong result. I tested this by depressing the ALT key thereby turning the ALT off and normal function resumed.
Logitech wanted to replace the mouse so in the interim I used my MS Wireless Notebook 4000 mouse with Intellipoint. Thinking this was a Logitech problem, I was surprised when the same malfunction occurred.
FYI: Latest drivers and SW are being used, Intellipoint and Setpoint "never" resided on my system together so no chance for conflict, I performed clean installations disabling the AV beforehand and have totally ruled out the Sonicwall because if this was the issue, I'd be having more than mis-assigned keystrokes as problems. Further, when I return all mouse buttons to their defaults, the problem goes away; completely!