Bug still present in 14w31a. Hopefully this gets fixed soon.
Dan, I can confirm the facing south data. I created a new world in 1.7.10 and planted four of each tall flower, one of each facing a different direction. Upon loading the world in 14w30c, three of each flower uprooted, the ones remaining were south-facing blocks.
I'm sure, I never load this world in snapshots unless I load it from a copy. I'll try a few more things and report back.
Edit: When I say "a copy of my world," I mean I copy the world save in .minecraft/saves, so it has all of my buildings and whatnot. Doing the "re-create" option in-game does not affect flowers, the only ones that break are those that I've placed.
I created a fresh world in 14w30c (seed -298304267424731851), flew east to 410 80 201 to a sunflower plain. Reloaded the world on 14w28b, flowers were fine. I knocked down and replaced some of them. Reloaded the world back in 14w30c and the ones I had replanted were gone.
Edit 2: Seems to be a problem that was introduced in 14w29a. All previous snapshots load the plants fine in previously made worlds.
Still occurs in 14w30c.
In my testing, I made a copy of my 1.7.10 world, then loaded it directly to 14w30c. Flowers still get uprooted.
Requires replaceitem command to do.
Bug still occurs in 14w30a as well as 30b. Still does not affect all plants, but same plants are uprooted in all tests I have done. All uprooted flowers were placed, does not occur for naturally-generated.
Can also confirm, from 1.7.10 to 14w29a. Does not break all flowers, but also affects certain flower pots with plants inside.
I know I'm starting to sound like a broken record, but bug is still present in 14w32a.