Changing parallel states causes properties to be reset

I have got a state machine with 5 states: Root, which has two children groupA and groupB. Root uses QState::ParallelStates, so groupA and groupB are parallel.
Both group have two child states, "on" and "off", so there is aOn, aOff, bOn and bOff.
Each of these states assigns a property of a global object:
aOn assigns the property "a" to "true"
aOff assigns the property "a" to "false"
bOn assigns the property "b" to "true"
bOff assigns the property "b" to "false"

Now, when changing from bOff to bOn, that causes the global "a" property to be reset, even though
none of the a states were touched!
The configuration of the state machine shows that groupA is still in the same state. So triggering a transition
in groupB somehow causes a property assigned from groupA to be reset again.

Expected outcome: Triggering a transition in one child of the parallel root state should not change any properties in the other child of the root state.

The attached example is a minimal testcase in one file.