problem cooking quinoa in stock

Quinoa has definitely become my go-to grain substitute, and its ease of cooking has proved pretty foolproof for the years I've been using it. I bring water to a boil, simmer it for 12 minutes, and let it sit until all the water's absorbed. But whenever I attempt to cook it in stock, it never cooks! After 12 or even 15 minutes, there's just a pan full of glop with no indication that the quinoa intends to absorb the liquid at all.

I've never seen any variations in recipes that call for any difference in cooking when using stock, and considering the number that suggest using it, I'd like to think this might be anticipated. Has anybody else encountered this problem? (By the way, I live above 5,000 feet, if elevation might have anything to do with it.)