Create a freestyle job and let it run on a label expression that contains blanks, e.g. "label1 && label2"

In Script console get the label:

l = Jenkins.get().getLabel("label1 && label2")
l.reset()
println(l.name)
println(l.getTiedJobCount())

The output is 

"label1&&label2"
0

Note that the blanks are removed when printing the label name.

The problem is that the method getTiedJobCount() loops over all jobs and then just does a simple String comparison of p.getAssignedLabelString() with the label name.