This seems to be happening to me pretty often and I don't remember it ever being reported before. Didn't find anything when I looked around for a while either.
Quite often when I try to plant a seed bag on cropsticks, it plants. The seedbag disappears from my inventory. However, when my inventory is updated, the seed bag reappears, and if I log out/in, the cropstick will be empty again. Sometimes this will happen upwards of ten times before I can get it to actually plant. Once they're actually planted, things work fine. I also didn't notice any issues when I was just planting regular seeds/reeds/netherwart/etc.
Update: it seems to work when there is an odd number of players on the server? That doesn't even make sense. Nevermind. It just seems to fix itself sometimes when players log on or off. But only sometimes.