Seems quite few people thought that was a bug already. This thought never crossed our mind when developing though.
I think it because they never got a blank images in any other slots before, just like me
Anyway how many blank images in each reel? Just tried it again and I saw there are 2 blank images in a row (3rd reel)
http://prntscr.com/7adiq5Is that blank or unloaded image (remarked as "second blank")?