While playing in Adventure mode while on my multi-player server, I encountered a single zombie in a house during the day. I retreated and the zombie chased me out into the sun, catching fire. Soon afterwards, zombies began to rain down from above, increasing the number of opponents dramatically.
Only once I moved a significant distance from the nearest burning zombie did the zombie rain end.
I have this on video, as I was recording a Let's Play when it happened.
Duplicate of MC-14683, please use the search function to see if your bug has already been submitted. Currently over 55% of tickets are being closed as duplicate.