I believe I have the same issue. Maybe two weeks ago I updated ARD along with one or two other software updates from the Mac App Store, and ARD always stays there, saying that there is one update available with the red number 1, but when you click on updates, the download button is grayed out and says "Installed". I do currently have the most up-to-date version of ARD installed. I updated ARD on 3 Macs of mine, with 2 of the 3 having the same exact issue. Issue: Mid 2011 Mac mini, Early 2011 13" MBP. No issue: Mid 2012 13" MBA. All have the latest version of ML, ver 10.8.2, and all other software is up to date.
I cannot seem to find a way to reset this. I am guessing that if I uninstall ARD and redownload and install it, it may fix the problem, but I do not wish to uninstall the app to get around this. Any ideas anyone?
Thanks