The "Add to Panel" not working, when right-clicking desired Applications from MintMenu, seems to be a new development. My Mint Maya 13 live CD still has this functionality, but I no longer do, even after trying to delete all the folders that xenopeek suggested... and resetting. I have also tried "mintmenu --reset" to no avail. Before this bug started happening, I recently reinstalled Maya plus a complete "Restore Files" of my Home folder with the Backup Tool. The reinstallation is how I solved a blinking, shrinking mintpanel issue resulting from Backporting my Maya OS to reflect Nadia. Or, perhaps the panel issue resulted from other non-backport-related updates. Not sure, unfortunately.
Anyway, the workaround, at this point, is to right click on the mint/MATE panel >> Add to Panel>>Application Launcher>> etc. This fix works. Interestingly, I see Cinnamon people have a very similar issue when they decide to remove the "Panels Applet Launcher" from their panel.jaderiver