I tracked down the first incident (where the spawn's energy only increased by 10) in the history. Somehow the creep both deposited its energy and renewed itself in the same tick. I didn't think this was possible, both in my code and in general, but it did, and I just didn't notice at the time.
I assume something similar happened in the second instance, so I'm not going to track it down. Thanks, and sorry for taking your time.