I'm also having problems with mintUpdate!
The startup one
/usr/lib/linuxmint/mintUpdate/mintUpdate.py
doesn't show an icon, but mintUpdate on its own or from the menu does.
Perhaps it has something to do with the icons directory?
When I try to change the icons from preferences it automatically goes to /usr/lib/linuxmint/mintUpdate/tmp folder, but they're actually in the /usr/lib/linuxmint/mintUpdate/icons folder?
Also, another bug I see is "User will login in ** seconds" still shows in the login screen even after I unchecked Enable Timed Login.
I tried it with different values and it still shows up when unchecked, doesn't count down, just stays there.