A similar thing happened to me recently, and I can eleaborate a bit more as well.
We had guests staying with us for a period of 3 days, but during the visit they decided to book for another 2 days. We normally charge a cleaning fee, and I didn't want to charge it twice, so I offered the rate for 2 days minus the cleaning fee as a direct offer.
The offered price that the guest saw was more expensive than the original...
Not sure if there is a glitch with this part of the system.