sometimes dates get prematurely saved with the value (e.g. year) cut off or short.
this is what i entered and is displayed ("1 March 2008") on https://test.wikidata.org/wiki/Q22 before reloading:
in the history, "Changed claim: Property:P121: 1 March 200)"
the issue especially happens if I hit save too quickly. It's as if the formatting is not completed when it saves.
this issue might also happen with other data types, like strings and wikibase item id values.