To reproduce the problem do the following:

We have the following layers defined:
default
default-shift
meta1

If the currently active layout is default-shift and i click on the meta1 the keyboard doesn't do anything. This is due to the fact that it tries to go to meta1-shift which doesn't exist.

The solution to this problem I propose would be to automatically change shift to inactive whenever a meta key is pressed.
What do you think about this approach?