Troubles with Encoding after convertig to InnoDB

Because of some performance reasons (especially when backing up) i converted the piwik tables to innodb.

After that i had some Problems with the encoding, like “stätte” which is now" stã¤tte " for old recods this is no problem (i can fix this manually), but also the new records look like this.

The DB is utf8_general and utf8 is also the charset, set in the piwik config.

Has anyone an idea how to fix this ?