problem with today's mission

i only have a problem with the watermelon one. i have done it twice now and it doesn't finish the today's mission quest for some reason. everything else works so far

This problem is already known; it's been posted in the Bugs section. I don't believe there's a solution to fix it; you'll have to wait for the Today's thing that appears tomorrow.

http://www.southperry.net/forums/showthread.php?t=13525
It's a bug.

Edit: ...geez, I'm slow at replying >_>