"Limit Kanji Per Day" not allows entering decimal number

In the days field of "Set Daily New Kanji Limit" (when tapping on the enabled "Limit Kanji Per Day" option) I cannot enter decimal numbers.

I cannot enter a point "." to get for example 0.5 days (it just does not enter the point when tapping "." on the phone keyboard) and when I use a comma "," instead, it registers the number as if the comma was not present, e. g. entering "1,5" changes it to 15 days.

Since the default value was 0.5 days I know decimal numbers should be possible. But after changing to an integer I apparently cannot go back to a decimal number. I would like to set the limit to 5 new kanji every half day, so being able to reset to the default value would already solve my problem. The true solution though, I suppose, is to allow entering decimal numbers.