? Incompatibility between R5 and R6?

I’m getting a strange result when trying to access docs updated by R6 client from R5 client.

A simple LS method like db.UnprocessedSearch doesn’t find the docs that were last written by the R6 client, but if I just open the doc in R5 and save it, the db.UnprocessedSearch finds them immediately.

Does this have some deeper meaning?