Replacement patterns produce wrong date filter

I am not sure if this is a Calander issue or a Views templates issue, but here is my problem:
I have built a Calander view from a template on a content date field. I also expose som other fields in the calendar. All this are ok.
One of the fields is a grouping field (count) I want to show the full list when clicking on this field. To do this I use the ability to 'Output this field as a custom link' and the 'Replacement patterns'. The date field is field_datum and the link text I added is like this:
/kalender_klass?field_datum_value={{field_datum}}+12%3A00%3A00
When clicking on this link it produced this: /kalender_klass?field_datum_value=2016-12-05_%2012%3A00%3A00
This patter {{field_datum}} produced the right date but added an underscore to it (2016-12-05_).

To be sure that this not is something linked to the date field itself I tested another link with the same field, but in an ordinary view, not a calendar view, like this: /test_datumfilter?field_datum_value={{ field_datum}}+12%3A00%3A00 and this produced the right filter:
/test_datumfilter?field_datum_value=2016-12-06%0A 12%3A00%3A00.

I hope someone can take away this little sign, so my nice calendar view can be even more useful.