Illustrator Scripting :: Making Unwanted Formatting Changes?

I picked up the following search and replace script online which works as inteded, except that it removes any italics I have and makes all of my text bold. Is there something I need to add/remove/replace to make it stop doing this?
 
Edit: It's doing even more in some files, including changing the size of my text. Also, it is only making these changes to any text box that has a string to be replaced.
 
function myReplace(search_string, replace_string) {
var active_doc = app.activeDocument;
var text_frames = active_doc.textFrames;

[Code].....