I'm using the following setup:

• WinXP slaves A,B,C
• jobs jA, jB, jC, tied to slaves A,B,C respectively using "Restrict where this job can run"

Assume all slaves are disconnected and powered off, no builds are queued.
When starting a build manually, say jC, the following will happen:

• job jC will be scheduled and also displayed accordingly in the build queue
• tooltip will say it's waiting because slave C is offline
• next, slave A is powered on by Jenkins and connection is established
• jC will not be started, Jenkins seems to honor the restriction correctly
• after some idle time, Jenkins realizes the slave is idle and causes shut down
• then, same procedure happens with slave B
• on occasion, next one is slave A again
• finally (on good luck?) slave C happens to be started
• jC is executed

It is possible that jC is waiting for hours (indefinitely?), because the required
slave is not powered on. I also observed this behaviour using a time-trigger
instead of manual trigger, so I assume it is independent of the type of trigger.
Occasionally it also happens that the correct slave is powered up right away,
but that seems to happen by chance. The concrete pattern is not obvious to me.

Note that the component selection above is just my best guess.

Cheers, Marco