TextInput and TextEdit don't seem to be working from time to time

I am using a TextInput inside a LisView delegate, that is supposed to make the data editable. Instead not even a TextInput (or TextEdit) that is not bound to anything allows input or modification of its contents.
Also, it seems that if you press the tab key, something goes wrong and a previously usable TextInput can never be used again.

All this happens when I use QML via a QmlView in my existing app. With the qmlviewer (in the bin directory) these things don't seem to happen... So when I looked at its source I found this:
contx->setContextProperty("qmlViewer", this);
Without that TextInputs don't work at all.