I cannot reproduce it. Screenshot below.
Please provide the following:

• Your OS version.
• A screenshot of your tweaker options.
• A screenshot of your taskbar properties.
• A screenshot where the bug can be seen.

Mostly fixed in v4.5.2.
The unfixed parts were filled as a separate report:
http://tweaker.userecho.com/topic/515930

Fixed in v4.5.2.

Fixed in v4.5.2.

Should be fixed in v4.5.3.
The issue existed since v4.5.1.8 beta (September 21, 2014), but unfortunately nobody has reported the bug until the final version was released.

Yes, the "Don't group pinned items" option has a couple of side effects. Additional example:
http://tweaker.userecho.com/topic/314270

Currently I don't plan to fix those, as I believe that they are not serious enough compared to the amount of required work to find a solution.

v4.5.1.8 beta fixes most of those issues.
The only remaining issue I'm aware of is that Taskbar Inspector doesn't show an icon, and sometimes doesn't show a correct title.

A duplicate of this, please see my reply there.
tl;dr should be fixed in v4.5.1.8 beta.