Okay, CJ, I consider this a minor bug, if this is a known problem and was already refered to somewhere just kick me. ;D
Basically the problem is that in the GUI, INV,... etc tabs of AGSEdit, when you hit the "edit script" button, (I think) the editor just search from the global script the first occurance for the function name, (for example in GUI tab, that searches for interface_click), and displays the content that follows, problem arises if the search text appears before the real declarition of the function.
You may try out this (http://www.strazer.net/ags/quitprob.zip) to confirm the problem, load up the game, go to GUI tab and hit "edit script", nothing's there, but the function was there in the global script, that's because the text "interface_click" appeared in a comment inside on_mouse_click, which was placed earlier than interface_click.
Worst of all, it also affect the game, probably caused by some problem in compiling the script, that for example some of the parameters won't get passed correctly, for example in that example on GUI5, the variable button always equals 1, no matter which part you click on the GUI.
You can read the original thread in full detail here:
http://www.agsforums.com/yabb/index.php?board=6;action=display;threadid=11423;start=0#lastPost (http://www.agsforums.com/yabb/index.php?board=6;action=display;threadid=11423;start=0#lastPost)
Ouch, nasty - thanks for researching the bug, I'll get it fixed.