Noticed this too: mintupdate is set to refresh every hour, yet I know there is "mint-translations" updated. Icon still green, until I open it, give it privilege to let it retrieve and parse the APT lists.. and then show the proper icon and the update.
I'm thinking it just can't have privilege, "doesn't run on sudo" until the user asks for it. Just adding "sudo" in it's command (control panel > applications at startup) doesn't do the trick here..
Proud Linux Mint Debian user since 04/2011
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Somewhere between Linus Torvalds and Richard Stallman