Steps to replicate the issue (include links if applicable):
On item https://www.wikidata.org/wiki/Q4115189

• Manually try to input "-29 FEB 45" on the P585 date field, with the Gregorian field

What happens?:
*-1st March 45 is shown

What should have happened instead?:
*"-29 FEB 45" should have been shown

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):
*If you send by Quickstatements,

Q4115189	P585	-0045-02-29T00:00:00Z/11

the result is correctly shown on P585 as -29FEB45.