In our ever-increasing quest to save water and only flush the smallest amounts of water this happened to our builder's toilet plumbed in sub-floor area.
DH & I noticed the bowl was filling too much when flushed, & a lovely (::hyst:: ) brown water would appear some time later. There is about 1mt of sewer pipe before it drops down a steep hill so block was close to loo. Asked plumber about what/how it could be blocked & said some times too much paper with half flush water it doesn't all get away. With the brown water & stink appearing I don't think it was just paper! I have often wondered with the super efficient toilets just how far the goodies travel with minimum water. Maybe we need to save loo paper too