Use of Prototype's Element-methods (like this.up("form"))
In /views/issues/_list.rhtml for example you use "this.up('form')". Actually the up-method is not available on the element itself, but only by the element, when it is returned by the $() method.
Quote from the Prototype-Documentation:
Prototype adds many convenience methods to elements returned by the $() function.
So, the correct way would be using: $(this).up('form') or Element.up(this,'form')
In IE7 the up method is actually not available on "this". In your case it's working "accidentially", because there is a call to $$('.hascontextmenu') executed somewhere in context_menu.js during page load, and by that the up-method is added to all DOM elements.
To better understand the problem check out this example (make sure to set the correct path and filename to prototype.js)