Stop casting question

So, I'm trying to use stop casting to interrupt my heals and begin a new one, however, I am having a problem getting it to work properly. The stopcasting is only working for every other cast. I've tried it in two different setups.

First one was just making /stopcasting its own macro and binding it to a key. It worked every other cast. My second attempt was with the clique addon and I made the stopcasting macro built in with a /cast macro for my gh 7, again every other cast it would work. Am I doing something wrong or is this not something this macro can do?

By every other cast I mean the following:

Start casting
use /stopcasting, spell stops casting
Start casting
use /stopcasting, spell goes through
Start casting
use /stopcasting, spell stops casting
start casting
use /stopcasting, spell goes through

I'm using quartz to time my interrupts but it doesn't really matter when I hit the macro on the 2nd attempt the spell always goes through.