Add Content to Batch button does not work - using 8.3.2

[snapdesign]

I have what looks like a bug with this tool.
I've successfully installed the migration tool on both legacy version and the most up-to-date version of concrete (8.3.2). I created a batch and exported xml content successfully from the legacy site and created a new empty batch in the new site. But when clicking on the 'Add Content to Batch' button, it does nothing. It does not show the pop up dialogue box to upload the xml file.
Can anyone confirm this is a bug? I am testing this on a sub-folder - would this make a difference?