The difficult part with your ProximityGrenadeTouch function is there are so many return statements which MIGHT end the function, and the bit of code that makes it stick to the wall is at the very end.

I would recommend you add some dprint statements to the function after each "checkpoint" - each place where the function has avoided a branch that contains a return. Then you can check how far execution gets through the function when you throw one against a wall, and deduce which exit is being taken unexpectedly. Two tips
a) pull down the console as soon as the bomb hits a wall for the first time, as you'll get a huge pile of debug messages if you let it bounce all over the shop first
b) remove the debug statements once you have solved the mystery, or they will be a pain in future