System Recording with the same two system sounds can't be saved

Steps to reproduce:

1. Log into FreePBX
2. Go to 'Admin/System Recording/Add System Recording' /admin/config.php?display=recordings&action=add
3. Enter a Name (e.g. Partner New Number)
4. In Add System Recording, enter digits/0
5. add another digits/0 System Recording
6. Press Submit

Expected behaviour:

1. Popup regarding the Conversion pops-up
2. System Recording gets added

Actual behaviour:

1. Popup regarding the Conversion pops-up
2. Buttons get disabled, nothing happens after that

Additional information:

The second recording doesn't get a play-button which points to something going wrong. It doesn't matter that the two entries are in sequence, it also happens when a number of other recordings are between them.

When pressing Submit and after confirming the pop-up the following JS-Error gets logged to the console:

TypeError: Cannot read property 'length' of undefined

Expanded in the console (not really readable but for future reference if somebody searches for the error message, screenshot attached):

Uncaught TypeError: Cannot read property 'length' of undefinedm.extend.each @ jquery-1.11.3.min.js?load_version=13.0.124:2(anonymous function) @ recordings.js?load_version=13.0.124:57m.extend.each @ jquery-1.11.3.min.js?load_version=13.0.124:2(anonymous function) @ recordings.js?load_version=13.0.124:56m.event.dispatch @ jquery-1.11.3.min.js?load_version=13.0.124:4r.handle @ jquery-1.11.3.min.js?load_version=13.0.124:4m.event.trigger @ jquery-1.11.3.min.js?load_version=13.0.124:4jQuery.event.trigger @ jquery-migrate-1.2.1.js?load_version=13.0.124:493(anonymous function) @ jquery-1.11.3.min.js?load_version=13.0.124:4m.extend.each @ jquery-1.11.3.min.js?load_version=13.0.124:2m.fn.m.each @ jquery-1.11.3.min.js?load_version=13.0.124:2m.fn.extend.trigger @ jquery-1.11.3.min.js?load_version=13.0.124:4m.fn.(anonymous function) @ jquery-1.11.3.min.js?load_version=13.0.124:5(anonymous function) @ pbxlib.js?load_version=13.0.124.1464848428:130selectorSetHandler @ jquery.selector-set-0.1.8.js?load_version=13.0.124:59m.event.dispatch @ jquery-1.11.3.min.js?load_version=13.0.124:4r.handle @ jquery-1.11.3.min.js?load_version=13.0.124:4