Unfortunately the orders of precedence used in different subjects (computing, science, etc) and languages (Perl precedence is mostly based on C's precedence) vary too much, yet are similar enough that people can make (sometimes-wrong) assumptions about what the order will be.

My background is sciency rather than computery, so I've seen several such problems, which are essentially arising out of sharing part of a language -- the concept of operator precedence exists in both the 'maths-language' and the 'perl-language', and means almost the same thing in both but with subtle differences which will be missed if you're not fully fluent in both languages.