Open Attachment option in Mail opens incorrect invite in Calendar

My issue: if I double click or use the Open Attachment option in Mail for calendar invites, an invite from 2 years ago opens in Calendar for me to accept. If I use the Add to Calendar function, no problem & reads like it should do.

I upgraded to ML about 2-3 weeks ago and Mail was spectacularly painful with the merge from SL not working at all. Calendar seemed to be ok, however this usse has started to appear in the last 24 hours.

Ivites can be accepted no dram using the iPad or my wifes iPhone just seesm to beon the Mac that its a problem.

Any thoughts/ideas/fixes would be great.

Cheers.