Ubuntu behaves as if I have two clipboards

My Ctrl+V produces a different result that RightClick+Paste

I can't reproduce this, it happens randomly, so I can't specify the circumstances just yet. I will as soon as I can make it happen all the time.

Please advise!

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 10.04.2 LTS
Release:    10.04
Codename:   lucid

X actually has three clipboards. Highlighting text moves it into one clipboard (PRIMARY), then performing a copy operation copies it to a second (CLIPBOARD) (the third [SECONDARY] is almost never used). The two paste methods are using different clipboards, which is causing confusion on your part.