Syncrepl: why would this happen?

Running 2.3.32 with the patch for added sync logging, I got this message:

Jan 15 18:51:14 wwsv04 slapd[7879]: Entry uid=example,ou=example,dc=example,dc=co,dc=nz CSN 20070115055002Z#000000#00#000000 greater than snapshot 20070115051233Z#000001#00#000000

This particular record gets an update every hour at *:51, but the message has only appeared once so far, and this version has been running since Friday.

It seems perfectly reasonable that the CSN with the later timestamp is greater than the earlier one, so why is it telling me this?

This is on the provider, which in turn gets its updates from the master server via slurpd. (a temporary measure until we can upgrade the master server)