As shown in the images above, grinding lemons in a quern overtop a drum makes fruit mash and a "blub blub blub" sound, yet no lemon juice appears in the drum.

Update: Try closing and reopening the world (in the current release you'll also have to close and reopen Minecraft to do that, though that's been fixed in dev). Once that happens, if this is the bug I think it is, you should be able to do it.

Also, this is assuming that you originally placed the drum and then immediately tried to quern it without closing and reopening Minecraft

Regardless, I think this is fixed. If you're so inclined, and it isn't fixed after the new update, please let me know.