Hi Cyril, thanks for the report.
Bug reports should go into the Code site at
http://kalendar.googlecode.com.
I'm also not quite sure what you are experiencing is a bug. I'd have
to see more.
That being said, the current javascript calendar is going to be
replaced with a jQuery date picker in the next release. If it is a bug
it is not likely to get addressed. My recommendation is to completely
remove the jscalendar and use the CF 8 date picker if you need to go
that route. Feel free to post as much info as you need to here so that
anyone else who runs into the issue might be able to better
troubleshoot it. :)