Wow, I broke it. Level 7, big room at the top of a long ascent lined with cannon-rocketplatform-cannon on alternating sides, headed up and left to the top left corner of the map, whereupon it froze, more or less. I was still able to "fire," inasmuch as it would take away snowpower if I hit space, but nothing moved. Could still turn the music and sound on and off and such, but there was no more gameplay to be had without a refresh.
I like this game a lot, that said. One of your better offerings.