[exim] Gmail frequent DKIM failures

Before I start investigating closer, I want to ask whether anyone experiences also frequent DKIM signature failures at messages sent
from Gmail. On my server, around ¼ of received Gmail messages do not pass the DKIM test with "body hash mismatch" failure. Those
message are no forwarded email, they come directly from a Gmail server. And they are also no fakes - I verified that they came from
genuine Gmail senders.

Except of Gmail, body hash mismatch is otherwise quite rare in our logs, so it does not look to me as if there were problems on our
side. On the other hand, I searched the web and did not find anyone else complaining about Gmail DKIM, which could mean the problem
is on our side after all.

Anyone?

Thanks,
Ivo Truxa