it happend while playing I was testing out my item elevator with no waterbuckets and torches on my hotbar. I spammed 'Q' while holding 'A' or 'D'. and the items in hand were all cobble one stack.

1: use hoppers to lead them all to one dropper pointing up.
spam-throwing 64 cobble in while going left and right (can be a little confusing).
2: after the droppers seem to be empty in one of the droppers is actually a waterbucket, and 2 torches!!

(maybe hard to re-create, crash-report is at the attachment, (forced crash F3+C), also, recent inventory is at the attachement)

at the images the situation is described. simple item elevator like:
http://www.youtube.com/watch?v=2wOW58fg8X4