Macbook pro and multibutton mouse

Hi there I’m really interested in more information on the matter.
I have a Roccat XTD which I used on my PC and now on my Mac. The problem is only while using the Mac
Here is the issue: I play a priest and I can’t seem to selfcast while targeting another player using my mouse. It does work if I click the actionbar or use the keyboard.
Example: I have assigned a healing spell on bottom left action bar matching action button 4, and it’s assigned numerical value 4. Then on the Roccat interface I reassigned one of the extra buttons to be inputting 4 as well.
That worked beautifully on my PC even when using the extra shift option button on the Roccat to double up the extra button function.
However it will not work on the Mac but only if I’m trying to self cast while targeting another player, if I’m trying to cast a spell on someone else the Roccat buttons work properly.
Example: I can target an enemy and cast SW:Pain but I can’t cast Renew on myself while still having said enemy targeted.
I know it’s long winded and I repeat myself but I just wanted to be clear.
Any idea?
Thanks.