a couple of candidates from BASH

[pasha-19]

uninitialized system variables that must be compensated for in application code everytime one uses them.
try

set -u
export PS4='$BASH_SOURCE:$FUNCNAME:$LINENO'
set -x
{and any console command}'

local variables, that are globally accessible as long at the function that created them is running ( from anywhere outside the function), and sometimes even longer depending on when garbage collection actually removes them all dependent on the distro's implementation of BASH. Not to mention inconsistent documentation at one point that claims local variables are C-like local; then later admits it is an opinion that they should be C-like local.