Sorry for the inconvinience Charlie, I am one of the developers of Wallch and I have to say that it isn't Wallch to blame about this misbehavior.
Wallch is built using the Qt framework and weird bugs appear on 14.04 on all the Qt based applications.
For example, I have noticed a bug in VLC: When I change the system volume, VLC's volume changes as well, Clementine's indicator appears and disappears all the time, and now Wallch seems to have problems as well like clicking the "Start" at Wallpapers tab not working and sometimes crashing the app, being able to open multiple instances from Unity, resizing of window seems to have problems as well, menubar sometimes not appearing, shortcuts like Ctrl+Q not working.
I had no problems with the Qt applications until I installed the NVidia drivers myself. Then all Qt based applications started to misbehave. Qt Creator (official IDE for developing Qt applications) crashed during startup with an X server specific error message.
This is truly frustrating for the developers. It is really sad to spend so many hours bug testing your application only to find out that the integration itself is broken and there is nothing you can do about it. Actually you can, but it is very frustrating to see so many things changing from the one to the other version of Ubuntu that require your code to change as well.
We had tested Wallch a lot of times, and we never had these kind of bugs.
I am on the process of fixing these bugs myself right now.
Please for more information see https://bugs.launchpad.net/ubuntu/+source/wallch/+bug/1310776