I assume you're talking about the Surevey Settings|General tab...
Yes, that's what I mean.
OK, the setting seems to affect only the full-featured survey, not the data entry screen.
This would seem to be a bug. In my opinion, the date format setting should control both survey submissions and manual data entry for a given survey (that's why it's survey-specific).
Please
open a ticket at the bugtracker and...
1. Give as much information as possible
2. Attach your survey. You can mark your ticket "private" so that only the developers will be able to take a look at it.
3. Provide step-by-step instructions how to reproduce the problem.
4. If possible/helpful please provide screenshots
Afterwards please post the link to the bugtracker so we can follow the progress.