... but why would the failure manifest as a CR at the end of $fname?
I suspect the text, created under Windows, has CRLF as the line terminator; running the script under Solaris the chomp is removing the LF but not the CR, so the CR was getting removed instead by the $fname substitution - but only when the substitution actually happened.
As for split, please take a look through perldoc -f split. First, note that the first parameter is shown as /PATTERN/; if you supply this parameter as a pattern (eg /,\s*/) it gets parsed as a pattern and does the right thing. If you supply a quoted string instead (eg ",\s*") perl will treat that first as a quoted string - in which case "\s" gives the warning, and gets converted to "s" - and the resulting string is then converted to a regexp further down the line.
You'll also find there far more than you ever wanted to know about the LIMIT argument.