I found a bug in the middle of a wave. Somehow the enemies, corpses and the labels showing the money and XP got freezed at their actual positions. Then I could shoot the enemies, but they didn't hurt. Also, no more zombies spawned from this point (but the wave meter continued to operate).
Nice game though!
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 "JumpingLine"){kind=icon}
 "Dude and Zombies"){kind=icon}
 "Doodle Devil"){kind=icon}