obscure mv behavior?

[ken at kg293.net (Ken Gosier)]

Hi, I'm getting a little funny behavior out of mv. Most times when I want
to move a directory, I can just do:

mv srcDir trgDir

and everything's fine. (That is, srcDir will no longer be there, and now I
will have a directory trgDir/srcDir.) Sometimes, however, I get the error
message:

mv: srcDir is a directory

I haven't been able to figure out the special circumstances under which I
get this message. (It happens randomly, as far as I can tell.) btw, I'm
running on Solaris 2.6. Also, if I explicitly say:

mv srcDir trgDir/srcDir

then it works correctly. Does anyone know what's going on here?

-- 
Ken Gosier
ken at kg293.net
ken_gosier at yahoo.com