Today it behaves differently. Now it is only allowing me to create one directory with no subdirectories under it. All of the following work:

 $diss = "\\bleen\\";
mkdir $diss,0777 or die "can't make dir: $!";

$diss = "\\bleen\\";
mkdir "$diss",0777 or die "can't make dir: $!";

$diss = "\\bleen\\";
mkdir ($diss,0777) or die "can't make dir: $!";

$diss = "\\bleen\\";
mkdir ("$diss",0777) or die "can't make dir: $!";
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If I extend my directory structure, it fails. For example

$diss = "\\bleen\\duh\\";
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fails.
I know that there is more than one way to do it. I usually go the least terse route. I could test for the directory and create it if it doesn't exist. Then I could change into the directory and test for the sub directory and create it if it doesn't exist, but that seems like the long way home to me.