When I growed up melon seeds, it appears to seems 2 stem in the same place.
Then I break it and sometimes It drops one more seed.

Also occurs with pumkin seeds too

STEPS TO DO:

Simply plant a melon/pumkin seed

Grow it with bone meal

Note that the stem seems to be 2 in same place

Break the stem and you got 2 (or more in case of pumkin) seeds

Also I uploaded a video with this bug and screenshots I make before video

http://youtu.be/DgkFPnBHNvg

PS: Apologize my English