If I have Notepad++ running as administrator, I can't drag files from explorer on to it (they are rejected with the 'stop' cursor) and if I try to use the explorer extension right click 'Edit with Notepad++' it throws an error.
Opening the files using the Notepad++ 'Open' dialog, or even double clicking them in Explorer works as it should. (Note double clicking is not a solution as very few of the files I want to open are default to Notepad++)
I have UAC set to 'never notify'.
Using the hack where UAC 'admin approval mode' is disabled fixes the issue, but kills the ability to use Metro apps.