bug report and a support case and see what results you get.
When someone from Zimbra declared that they won't fix 3rd party bugs even if it's a critical component of Zimbra, it does raise an alarm and got us worried.
I think if Zimbra is responsible enough to fix 3rd party bugs if it is critical enough to affect Zimbra operation, then a more accurate and assuring statement should be something like this:
Zimbra will fix all critical bugs, be it from Zimbra coding or 3rd party coding used by Zimbra. The exception will only be 3rd party minor bugs that won't affect Zimbra operation in anyway.
It's not a silly comment because someone in this forum stated that Zimbra won't fix this bug, not because it is a minor harmless wanring, but because it is a MySQL bug, not an Zimbra bug, isn't it??? :P
I think you misunderstand what these forums actually are - they a Community support forums and not official Zimbra Support. People that post here do so in their free time and voluntarily. Any comments made on these forums are the opinions of the person posting, they do not represent Zimbra (or VMware) in any way.
I've already said this but I'll repeat it, if you have a problem with this error message then file a bug report and raise a support case, that's what you pay for (as you've point out) and see what response you get.
I personally think that an warning message that is emailing out your root MySQL password is a critical issue! MySQL bug or not, you can certainly spend a few moments to at least filter it out for your users.
I haven't seen this error yet, but rest assured I would be very upset if my root credentials would appear in an email to me as plain text.
Aside from that, if it is just a benign warning message that has no repercussions, then just ignore it...