Leo,
I was able to reproduce the issue that you are seeing locally. I have opened a LabKey issue for this scenario:
https://www.labkey.org/issues/home/Developer/issues/details.view?issueId=18187

I haven't looked too much into it yet, but I suspect that the issue is related to the spaces being inserted into the required fields. It looks like when you try to do the insert from the browser via the "Insert New" action, the spaces are trimmed off but when inserted via Rlabkey they are not.

-Cory