I have Ubuntu experience, but not Linux Mint. I have dealt with the Catalyst / FGLRX drivers for my Radeon HD 6850 in Ubuntu (the base of the Linux Mint 15 distribution).
Only thing I can find with googling is that it says openGL may cause problems with some drivers. You could try to disable Cario Dock's use of openGL. How did you install the Graphics Drivers? Did you use Linux Mint's automated system or did you use the versions on AMD's website? I would recommend using AMD's version rather Linux Mint's / Ubuntu's version.
Alternatively, you can try to purge the window managers or restore default settings or change window managers, but I don't have much experience with that and I am not sure to what extent they will help. You should also ask in both Mint and Cario Dock forums to see if they have any additional advice.
For removing Catalyst / FGLRX and restoring open-source drivers in standard Linux Mint 15 based off of Ubuntu::
You should be able to remove the old drivers from a terminal (either ALT+ Control + F1 or F2 or F3 or F4 if they left terminal access using that method). Otherwise, if there is a safe-boot mode in advanced listing directly under Mint under the grub startup (I'm hoping one of these methods are similar to Ubuntu). Otherwise, find some way to access terminal without being in the desktop environment.
Then follow the removal instructions for Catalyst / FGLRXhttp://wiki.cchtml.com/index.php/Ubuntu_Raring_Installation_Guide#Removing_Catalyst.2Ffglrx
You won't need this unless part unless you are using Linux Mint Debian Edition (LMDE) (I have no experience with LMDE, but it's based on debian, so the following should work):
Find a way to get to terminal then follow the linkhttp://wiki.cchtml.com/index.php/Debian#Removing_Catalyst.2Ffglrx
Once you are using the open source drivers, restart and see if it fixes the issue with cario dock. If it does, you can try using AMD's latest drivers from their website if you want, or just leave it at the default open-source drivers (although you will likely need to disable openGL if you haven't already). Back in Ubuntu 12.10, I used the wiki.cchtml.com's manual install and it worked. I did encounter the Underscan issues mentioned in the help.ubuntu.com, so I'm including the link.http://wiki.cchtml.com/index.php/Ubuntu_Raring_Installation_Guide#Installing_Catalyst_Manually_.28from_AMD.2FATI.27s_site.29https://help.ubuntu.com/community/BinaryDriverHowto/ATI#Manually_installing_Catalyst_13.4