Unhelpful behaviors in 4.2.10(1)

[Linda Walsh]

File1:
sdf:
Ishtar:/tmp> more sdf
#!/bin/bash

_prgpth="${0:?}"; _prg="${_prgpth##*}"; _prgdr="${_prgpth%/$_prg}"
[[ -z $_prgdr || $_prg == $_prgdr ]] && $_prgdr="$PWD"
export PATH="$_prgdr/lib:$_prgdr:$PATH"
shopt -s expand_aliases extglob sourcepath ; set -o pipefail

. backtrace.shh

. sdf2
--------------------------------
file2: sdf2
#!/bin/bash


[[ $# -ge 2 ]] && echo weird

--------------------------------
running:
Ishtar:/tmp> sdf
 Error executing "[[ $# -ge 2 ]]" in "main"
    at "./sdf", line "4" (level=0)
---


So why am I getting a backtrace (and how do I make it put out the right 
file)?
I thought rather than something just dying -- it would be nice to know 
how it got there... so...backtrace... but the line it is complaining about
is in "sdf2" --- and WTF?... how is testing a number an error that would 
cause a
exception?

(if this was running under -e, I presume that if statements that are 
false now fail?... )...I thought complex statements were not supposed to 
fail

POSIX really F-U'ed on this one... go back to bash 2's "simple 
statements"...
having conditional statements fail is going overboard...
I mean it's an explicit check to avoid an error condition...so, of course,
such checks are now errors?!?!?!....ARG *hitting head against wall....***

file:
backtrace.shh:

>  more /home/law/bin/lib/backtrace.shh
#!/bin/bash
function backtrace {

 declare -i level=0
 while {
     local cmd=$BASH_COMMAND
     local fn=${FUNCNAME[level+1]:-}
     local src=${BASH_SOURCE[level+1]:-}
     local ln=${BASH_LINENO[level]:-}
   }; do
     [[ -n $fn && -n $src && -n $ln  ]] && {
       echo "  Error executing \"$cmd\" in \"$fn\""
       echo "     at \"$src\", line \"$ln\" (level=$level)"
       level+=1
       continue;
     }
     exit 1
   done
}

trap backtrace ERR
set -T