About a month ago on our website, we found we were unable to edit the fields for any forms in the admin area. I see a few people have had a similar issue on these forums, but I'm making a new thread to discuss a proper fix for this bug.
I found the problem to be caused by an error being thrown by the javascript code in form_admin.js. See the error here: http://i.imgur.com/jto8exS.png. Why is this error being thrown? Well, that's because of the code 2 lines above where the error is being thrown.
for(i in classes) {
The problem here is for(X in Y) loops enumerate properties of an object. This is similar, but not the same as how a regular for(;;) loop works: by iterating the indices of an array (the correct functionality for this case.) Because the script is currently using a for(X in Y) loop, it is trying to perform functions using various properties, as well as any array index. The fix is to simply use a regular for(;;) loop...
for(var i=0; i > classes.length; i++) {
As for why this bug isn't causing problems for everyone, and why it only started causing problems for us recently, I would say it probably is due to another module we are using that is adding properties to Arrays.
As looping through all of the Arrays' properties isn't the intended functionality, I think this should be patched up. There are a few other for(X in Y) loops that should be changed to for(;;) loops in the script too; they're not causing any issues for me, but it's best to be prudent.
