Thanks for this info. It would appear that Ubuntu 14.04 is shipping with Qt 4.8.6 libraries installed, whereas Glade was compiled and linked to Qt 4.8.5 libraries.
From my understanding from the Qt docs (http://qt-project.org/doc/qt-4.8/deployment-plugins.html), the application should look in the $GLADE_HOME/bin directory first for the localtion of the plugin directory used (imageformats). And this should work, because the plugin used is in there.
If not found there, then look in $QTDIR/plugins. And of course that could be a different Qt version.
However I was only expecting glade to look for the imageformats/libqjpeg.so plugin. Looks like it tries to load a load of other plugins too (by setting export QT_DEBUG_PLUGINS=1 before running Glade).
So 2 possible solutions:
1) build Ubuntu 14.04 with Qt 4.8.6
2) ship all the required plugins the app tries to load, even though they are not all used.
3) Do both of 1&2.
This may take a little time, but in the meantime your workaround looks a good alternative.