I think you use a very old Joomla and VM release 
Most of your code is obselete ! 
I think all this is solved in VM3 and vm 2.6.
Hi Studio - as per my msg. 3.0.16 IS still broken for this specific bug, which is my current VM and seeing that newest releases can have bugs I wasnt going to upgrade to find out if the bug had been fixed and bring more bugs in.
THOUGH here is the big tip for the day. Some of my developers had no idea about it, and others said they were too busy to find a solution. I spent a lot of time and some money to find a solution that was ridiculously simple.
While you can put meta title data into the VM 3.0.16 edit fields for individual products and they ARE used in the browser title as is the plan, the Category meta data IS NOT. Of course since the Categories are typically also replicated as MENU links on an ecommerce site you can just go into each Menu link you want to add your own seo title to and do it from there instead. I think that when VM category metadata fields work (future releases) they will probably over-ride the MENU category data ... so I just have to make sure that only the MENU data is filled in, or keep the data in the VM category fields exactly the same.
NOTE the only concern I had was that I have four or so menu's that use category links because of template design ... and have found that if I fill in the MAIN MENU category meta title data it replicates to all of the other MENUs. As long as the Category words are the same which you want to avoid possibility of google considering there are duplicate pages.
ANYWAY. Hope that helps others out for this short term fix. NO core code hack, and actually using the JOOMLA field positions rather than the nice to have VM ones that didnt work in the version I (and the original poster) had.