The issue goes like this:

Lets say you have a 3-6 days reservation type. It works fine if u select the days in the same month.
BUT if you selct, for example, at 30 of January as the check-in and then click "Next month", then the restriction is not working and you can select more that 6 days.

Example: Check-in: 30th of Jan
Check-out: 20th of Feb

This is a BUG.

Hello, thanks for your notice. We will fix it in next release.