There does appear to be a JIRA entry for this, but it mainly seems to be being ignored.
The effect is completely random, and different each time I log in, but sculpties will be rendered entirely in alpha when I zoom in on them - it's like a LOD issue in reverse! It doesn't affect all sculpties with the same map just a random selection of them. I can select the invisible sculpties so I know they are there.
I've tried all the currently available client versions, and updated my graphics cards drivers. The card is an nVidia 285GTX. I've also tried different graphics preferences both in SL and the nVidia control panel.
Can anyone shed anymore light on this issue? How many people is it affecting? Is it being fixed? is there a work around? I'm currently working on a job with a lot of sculpties and it's actually... impossible as you would imagine, since I can only ever see a random selection of my prims at one time.
UPDATE: I have reverted to my old nVidia 8800 card, which is even on the list of supported devices and am STILL having this issue.