I also have had problems with 'append', though I tossed it up to incorrect usage and didn't look into it.
used it to replace instances of (array1 + array2).
Such as: (array1 append (array2 append array3))
Does not seem to work for those uses, I am guessing I just don't yet understand 'append'.
pushBack only works for arrays created in script language.
for instance, you cannot do (allDeadMen pushBack [man])