Error when trying to update an issue which has an original estimate 30m

I created an issue with an original estimate of 30m. When I try to edit/update this issue I get the following error meassage:

"The original estimate specified is not valid"

The Screenshot shows that the original estimate of 30m is transformed to the value '0,5h' which triggers the error.

This startet happening, when we changed to the time tracking format 'hours'.

Character encoding: UTF-8
Indexing language: german
Default language: Deutsch (Deutschland)