Thanks for reporting! Thats a weird issue, seems to be android only. I could reproduce it as well on my Nexus 7 this morning...
Andy, It seems to be after you swipe for anything. like after 4 common, uncommon, or rare items towers and potions.
Either I'm incredibly bad at remembering things and blind, or the ability to do 1000 waves seems to have disappeared, I can't see a way to do more than 200.
With the new version, the ability to increase the amount of waves has been removed. There is now a real test after wave 200. It's a truly endless mode.