Use a newer version, your IMP version is badly outdated.

IE 7 Bug. Occurs near setKeyBindings inside of javascript.inc and the 
corresponding function inside of keybindings.js.



I noticed inside of keybindings.js that you're using an array to hash 
keycodes.



In IE 7 (and possibly other browsers) if you want to do hashing it's 
better to use an object because:



var a = [];

a[0] = 'foo';

a[100] = 'bar';



Will result in the array being populated with nulls from 0->100.



Of course, maybe you're modifying the array prototype or something 
like that and are working around this.



I tested the following change:



var _keyMap = new Array();



to



var _keyMap = {};



With improved results.