I usually use for entry date values in spreedsheet slash on numeric pad, but in current release version don't work. I must use classic "dot" character as separator date, month and year. It does not matter if cell format is set to "general" or "date".
This problem should be fixed with fixes for "Bug 52240 - [Task] EDITING: Incomplete Date values are no longer detected"
I mark this one INVALID because too much info is missing.
Please feel free to reopen this Bug if you still see that problem with LibO 3.6.2, but then please contribute complete useful info due to http://wiki.documentfoundation.org/BugReport> (Localization, sample document, ...).
*** This bug has been marked as a duplicate of bug 52240 ***