It's happening in 7.54 also. It happens for $hfind but I can't make it happen for $findfile or $finddir. When this glitch happens, it's falling through to the next line with $error defined without mentioning a line number, instead of jumping to the :error label.

alias testerror {
  echo 5 -a beginning value of $ $+ error is: $error
  ; echo -a $null 
  ; noop  $findfile(.,*,0,1,if $false noop)
  ; noop  $finddir(.,*,0,1,if $false noop)
  noop     $hfind(rr,i*,0,w,if $false noop)
  echo 6 -a falling thru. this will not contain a line number: $error
  echo 3 -a entered :error at line $scriptline with $ $+ error set to: $error
  if ($error) {
    echo 4 -s from /testerror:  $v1