It is a one way trap. Very annoying.
According to here Set MMC 3.0 Console Options you should be able to reset it by changing the console mode to "User mode - full access" (but it doesn't work for me).
I think I can see the problem in C:\Windows\WinSxS\amd64_taskschedulersettings_31bf3856ad364e35_10.0.10240.16384_none_52eb75789f0a2f2 a\taskschd.msc
It is the bits in bold I think - they don't exist in any of the other (many) copies of taskschd.msc
but if I change it makes Windows think it is unsigned (and still doesn't work). Guess I'll try and restore it from somewhere and see if that works. Grrrrr, what a PITA, that will teach me not to make a restore point
<ViewOptions ViewMode="Report" NoStdMenus="true" NoStdButtons="true" NoSnapinMenus="true" NoSnapinButtons="true" NoStatusBar="true" NoTaskpadTabs="true" ScopePaneVisible="true" ActionsPaneVisible="true" DescriptionBarVisible="false" DefaultColumn0Width="200" DefaultColumn1Width="0"/>