Sometimes my KM catches alike problems.
As a rule, this being connected with the content of particular page (and tab). So I simply close KM, then open prefs.js with text editor and remove line with the info about this tab
user_pref("kmeleon.plugins.sessions2.Previous Session.window0.count", 20);
Here you have to decrease number by 1, when editing - this tells KM to open 'n-1
Forum:
General