Question: When i click on the buy button in the software center it instructs me to login, however as i'm using Keepass for saving my passwords i would like to paste it in but it wont let me...

the same applies to gwibber when i try to input my facebook password.

it is possible to input manually but since i picked a long password this would take very long.

Unfortunately until now i couldn't find a solution other than just not logging in or stop using the password manager.
Does anyone have an idea?

Answer: 
I solved this problem by using keepassx instead of keepass.
If you tried pasting through the popup menu, well I'd say that is reasonable for a password field to have the Paste entry disabled. In some cases the keyboard shortcuts might work, so try Ctrl+V and Shift+Ins.