Minecraft 1.4.5, Snapshot 12w50a, Minecraft 1.4.6, Snapshot 13w05a
Mac OS X
Title says it all. Looking at the tentacles while the actual Ghast is off the screen makes them invisible when they should be visible.
Easier to reproduce if looking at the Ghast dead on.
This also seems to occur with other entities, such as item frames.
MC-1058 A dragon head is invisible if the entity wearing it is not in view