Comment # 5 on bug 1059438 from Tim Real

Sorry, I may have caused some confusion with the posted solution:

That poster's needs were slightly different - I just wanted 
 the behaviour disabled completely.

Thus, here is the ~/.Xmodmap file which I had to create,
 this solved the issue completely for me:

keysym Control_R = Control_R
keysym Control_L = Control_L

My current layout is US.

Again, I cannot stress enough, IMO the default behaviour
 is just plain wrong.
Something, possibly the Kernel, is making both control keys
 Multi_key compose keys by default. Not good.

Thanks.