Cannot decode qr images with Qtqr in UbuntuStudio 16.04.1

I installed qtqr and its listed dependencies (python-qrtools, pyton-qt4) using Synaptic Package Manager in a clean installation of UbuntuStudio 16.04.1.

I can make qr code images by typing into the qtqr gui. These images appear to be good (they scan correctly in my smartphone) but I can't get anything to happen when I try to decode using the gui.

There is in the gui an invitation to drop image files in the gui. I click and slide a file into the gui and expect to see the hidden data revealed. This does nothing at all - not even a sign of the file being accepted..

There is a dropdown box in the lower right side of the gui which invites me to decode a file. I navigate to the qr.png file and click to open. The selection box closes but apart from that absolutely nothing happens in the gui.

I have seen an old reference to python-zbar not being in old (10.04) versions of ubuntu. That is present in my installation.

I imagine I must be missing something simple somewhere. Any suggestions would be welcome.