So the answer appears to be the diode.  When it's in parallel with  
the transistor as the book shows, it causes the latching behavior.   
When I put the diode in parallel with the solenoid,  no more latching.

So now I know what's wrong, but not why it does what it does.  Can  
anyone explain why the transistor would stay on because of a path for  
current to get from E back to C?

mystery half solved,

darren

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