When I disable a job, I right-click on the job and select "Disable Job". When I want to enable the job again, I right click and select ... "Disable job" again?
RFC: When enabling a job again, "enable job" has to appear in the right-click menu.
Changing the world one menu item at a time

[EDIT]
This only seems to happend in the following scenario:
I Select ALL jobs in the job window. I right-click and select "Disable job". ALL jobs get disabled. I immediately right-click one of the ALL selected jobs again thus maintaining the selection, then "disable job" is still unchecked.
When I disable all jobs, click somewhere else so that the selection is cleared and right-click on one single job, the checkmark at "Disable job" is visible.
So it seems that the checkmark DOES work while selecting single jobs, but not multiple jobs.
[/EDIT]