I had Hudson configured with exactly one slave, and tied a couple of jobs to it.
When I deleted the slave, the 'Tie this project to a node' option disappeared
from my Job Configure page (as it should). However, all future executions of
those builds were all 'stuck' (as shown in the Build Queue). I believe that the
previously tied jobs were in fact still tied to the nonexistent node, because
when I readded the slave, the 'Tie this project to a node' option reappeared,
was checked, and tied to the slave. I un-tied the job from the slave, deleted
the slave, and the job executed again.