Does your ERP software vendor Cc you in the same bug database that their developers use? That can be more valuable.
I've had some really long waits too -- my
Bug 32536 – Zimbra too trusting of MIME-type sent by client really dates from March 2008 (it took two months to realize what the actual problem was) and is due to be addressed in 5.0.16 any day now -- but I understand that my issues aren't the only issues.
Making sure that your issue is tagged with your support case number (they don't always do that) and (as appropriate) lobbying for votes here do help.
32536 took a long time because it's really a Mozilla bug, not a Zimbra bug, and figuring out how to work around it safely is nontrivial. I don't know about your bugs.