I got an email from an end user with a similar problem. They have the latest service pack installed. They were using KOM's Customer Number Change addon. Here is their message. She did some unusual things, so it may be just a coincidence, but it is close enough...

Usually after using Change Customer Number I do a data integrity check in A/R. This happened on Saturday and the data integrity found errors. I started a rebuild, but interrupted the rebuild to check a customer account maybe this was a mistake?). To begin the rebuild again, I had to do another data integrity first, but it found no errors. Not being sure if I should believe this, I ran the data integrity again immediately, and this time it found errors. I ran the rebuild. Then another data integrity. The rebuild went fine, and the data integrity came up with no errors. This morning I discovered a customer with most of his history missing.