I don’t generally post on Sharepoint bugs, though I run into a lot of them at work. I’ll make an exception here because this is a nasty bug, and I wasn’t able to locate any descriptions of via Google. So if anyone else runs into it, this post might be helpful.
This bug manifested with a Sharepoint 2007 document library. This library had custom fields (columns, attributes, metadata, etc) like “group”, “tags”, “author” etc.
One day we were unable to see or edit those custom columns in the standard (web) view. It was as though they had vanished. We could see them in the Access/Excel-like “data sheet” view, so the data was there. We could even edit the values in that view.
It wasn't easy for our IT group to figure out what had happened. It seems that under some circumstances setting a field as "required", when rows already exist with null values for the field, will corrupt a Sharepoint list.
It can only be repaired, with difficulty using, Sharepoint Designer.
There is no fix date from Microsoft this bug. For the time being the required attribute value should not be used in a Sharepoint list.
There are worse things about Sharepoint (the world’s most inane file share and document management system) but they’re design flaws, not bugs. Up to now this is the nastiest SP 2007 bug I’ve personally experienced.