Import in custom date fields does not function correctly

Situation:
Trying to import attached file in demo system. Fields: First name, Last name, Email and testdate (custom field). First line contains headers. Date format dd/mm/yyyy.

Following behaviour is observed:

• After clicking 'import now' on preview screen the preview screen is shown again (once)
• Only the first two records are imported (consistent with two import now clicks)
• This is only an issue with custom date fields. When used with for instance birthdate it seems to work correctly.