Homematic: HMIP-SWO-PL rain counter shows wrong value

I am on openhHAB 3.4.2 and have connected my homematic devices via homematic binding.
In the homematic webUI the rain counter shows

The thing channel in openHAB shows

I would expect both values to be the same.

This is the same for me:

In openhab it got reset one week ago and I have no idea why:

I mean, I can live with that, but it would be nice to understand.