If you have a label expression like this:

!Node1

The Labels Dashboard shows that Node1's label is used by a job, but clicking on the link to see the actual job(s) does not show those jobs. It seems that the display of jobs that use a negative expression with a particular label (either /label/Node1 or /computer/Node1/linkedJobs) does not show those jobs. Even though the purpose of an expression like this is to exclude that label from builds, it would still be useful to be able to see where that label is being used in any way, even in a negative expression.