There is no reason for it to be an ethnic slur. The ***holes who did and still do persecute Pakistani's use the shorthand for the same reason a normal person would want to use it.Let's start again. People don't get upset because it's shorthand. In the UK it's an ethnic slur with a long negative history behind it. Like the n word.
Not to mention how a word is used is what gives it context. Its pretty easy to tell whats meant to be offensive and whats not. No one has used the shorthand in an offensive manner in this thread that I've seen.