Steps to replicate the issue (include links if applicable):

site = pywikibot.Site("test", "wikidata")
item = pywikibot.ItemPage(site, "Q229226")
prop = pywikibot.PropertyPage(site, "P97339")
claim = pywikibot.Claim(site, prop.id)
claim.setTarget("test")
item.claims.setdefault(claim.id, []).append(claim)
item.editEntity()
item.claims.clear()
item.editEntity()

What happens?: Nothing happens on the second call

What should have happened instead?: All claims on the item should be deleted

Software version (skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):