I couldn't reproduce the issue.
In general, "Open with" is a feature of Windows, but you have to hold Shift while dropping to make it work. The tweaker only makes Windows think that Shift is being held.
Try to turn off the tweaker, and use Shift. Do you still encounter the issue? If yes, then it's probably not the tweaker's fault.

Hi Guido, 

Unfortunately I don't speak German, but I've translated the text using Google Translate, and I understand that you like 7+ Taskbar Tweaker and find it useful. Thank you for the positive feedback!

I believe that it's possible to achieve this with taskbar properties if you're using Windows 8 or above.

Closing as a duplicate:
http://tweaker.userecho.com/topic/382920-after-wak...

Unfortunately, I cannot reproduce this bug. All I know is that it's caused by the autoupdate checker, and by looking at the reports you can conclude that the bug occurs only on Windows 7. Perhaps it's a bug of Windows, I don't know.

This is not the same issue as the one the pre-Windows 8.1 Update 1 version.
Please see my reply here:
http://rammichael.com/7-taskbar-tweaker/comment-page-17#comment-3660

v4.5.1

v4.5.1

v4.5.1

v4.5.1