Login picture / wysiwig editor icons are scrambled

Hello, I have updated my 20+ weblogs to 2.3.3 and now the login – picture and the wysiwig editors icons are scrambled.

I have searched for a solution but did not found one. I changed the settings for gzip. No change. I altered some code of the tynimce, as described here somewhere. No change.

Interesting is, this only happens at the hosting provider metanet.ch – not at my three others.

Has someone a glue? Thanks in advance.

smartpepe