In the xkey vmod documentation, keys in the pages headers must be separated by spaces and not comma.
"Alternatively you may instead use a single header with space separated values like xkey: 8155054 166412 234323."
So when varnish associate the keys to the pages, instead of "content-249" we have "content-249,"
eZPlatform is not able to purge the keys when a content is modified in BO.
You must change the EzSystems\PlatformHttpCacheBundle\Handler\TagHandler class :