The forceeditsummary option conflicts with a &nosummary=1 in URL. You will get MediaWiki:Missingcommentheader, but you cannot and should not giving any comment.
Please also see bug 17416 for issue with forceeditsummary and &summary= in URL.
Thanks.
Version: unspecified
Severity: enhancement
URL: http://de.wikipedia.org/w/index.php?title=Wikipedia:Spielwiese&action=edit§ion=new&nosummary=1