Menu bar clock not updating except when clicked

Hello. I'm having a really weird issue with my laptop (Macbook Pro, 10.7.4). In the last few days it's abruptly developed an issue where the clock in the upper right-hand corner will not update unless I click on it. In other words, it will display 10:00 steadily for forty-five minutes, but when I click the menu bar to get the Date/Time dropdown, it suddenly updates to 10:45, which it proceeds to continue to display until I click it again.

I've checked the Date/Time Preferences and they all seem to be right. "Set Date and Time Automatically" and "Set Time Zone Automatically" are checked, and both seem to register correctly in the preference dialog. The analog clock in that dialog also ticks along correctly but when it ticks over to a new minute, the menu bar clock does not change.

Out of curiosity, I flicked some of the options under "Clock" in the date/time preferences on and off...telling it to display the time with seconds doesn't change anything; the seconds remain as stagnant as everything else. Toggling it between a 12-hour and 24-hour display does cause it to update to the current time, but not to resume updating automatically.

All in all very weird, and is *really* throwing my groove off (you don't realize how much you come to depend on the computer clock until it isn't there). Google isn't coming up with any obvious answers...has anyone run into something like this before?

Much thanks!