Hi, Plaidthumb.
I bought some corn and nuked it not long ago with the same results. I'm thinking the corn looked like it was in need of a little more water shortly before it was picked.
When I used to grow corn, the critical watering time was about the two week period before it was picked. I used to irrigate then, in the late afternoon, on the advice of old farmers who had gardens in the area. That solved the problem for me! Think doing it at that time during that period of growth let the plant soak up enough moisture to make it through hot days without getting stressed and parched.

cooked some more tonight and no problem. Think I might've overcooked it.

I'll water it a bit more next year around picking time. Thanks for the tip.