I have been searching about (for) this for a couple of weeks :/ (I am a major n00b here, I tried Linux out about 10-12 years ago(RedHat when it was still free).. didn't like it, so went back to WinBlows... but tried Mint out starting about a month ago and like it much better now)..
This is only the second post I have seen about it though.. (I've noticed that anything similar hardly ever gets replies, but since you posted exactly the problem I have, I decided to get off my n00b butt and reply)..
Here is my screencap (ironically, I took the screencap from a Samsung too
I DO know part of the cause.. (Something about 3D acceIeration) am running nVidia GTX470 with 2 monitors.. as LONG as I don't activate my second monitor, I get a clean/smooth Cinnamon desktop. As SOON as I activate my 2nd monitor, it kills Cinnamon and goes to 'fallback'... and everytime I go back to 1 monitor and then try dual monitors again, it adds another taskbar :/
I am trying to find HOW to get rid of the extras now (ran across your post and wanted to jump in, not that I can help though)..
HOPEFULLY, since they can see it is not an isolated incident, someone will speak up and let us know how to get rid of the extra 'trash'.. :p
I really like Cinnamon a lot, but will give it up until they 'fix' it just so I can still keep both of my monitors running on Linux.
Anyway, let's keep our finger crossed that someone will assist
<edit>: lol.. I had to go back and edit.. obviously, this site doesn't take HTML Code