It's delayed evaluation of $1. The solution is to put it in quotes, i.e. "$1".

He's a shorter example:

$_ = '1a';
print( (/(\d)/ ?  $1  : 0), (/(\D)/ ?  $1  : 0), "\n");  #aa
print( (/(\d)/ ? "$1" : 0), (/(\D)/ ? "$1" : 0), "\n");  #1a
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At run time, the variable $1 is pushed on the argument stack twice, then print is called. Print evaluates each of its arguments, getting its string value, and at this point $1 evaluates to the first capture of the last pattern match.

Think of $1 being tied, with FETCH() being called (twice) from print.

Dave.