Minecraft 14w10b, Minecraft 14w10c, Minecraft 14w11b, Minecraft 14w17a, Minecraft 14w18a, Minecraft 14w18b, Minecraft 14w19a, Minecraft 14w20a, Minecraft 14w20b, Minecraft 14w21a, Minecraft 14w21b
Windows 7 64 bit, latest Java version 7 (build 1.7.0_51-b13)
EDIT: Now actually fixed with 14w25a!
Columns of vines growing down into (not placed into) the left-hand half of an inside corner will render out in the air when vines are already present on the right-hand side of the same inside corner.
In creative, place vines on both sides of an inside corner so that they will grow downwards and into the same block of air. Let some time pass. Observe that vines on the left side will pop out into the air instead of growing naturally. (See images.)
Reverting to 14w08a reverses the effect, causing vines to render normally.
Bug still present in latest snapshots. Not fixed.