Well what happened to me was the following, I had an Issuelist (migrated from a Wssv2) and was playing with the new opties that are available for a Multiline text fieldtype. I enabled the "Append Changes to Existing Text " function on a required field column. By doing this the values remained but everytime I edited an issue, while the field was filled in, the form requested that I need to fill in the field. This is not very desirable for a field that is only required to be filled in at creation time. So I disabled the 'Append Changes to Existing Text' and was then suprised to find out that for all the existing items the field values were deleted!!! Lesson learned : never (!) change the type of a (even it is an adjustment of the current type) field without making a backup or test it thoroughly!