QSortFilterProxyModel Q_Assert cm message.

I have a model(lets call it base model) on which various QSortFilterProxyModel are connected.
In the base model (hierarchial) I call beginRemoveRows and endRemoveRows(). This leads to a Q_ASSERT message from QSortFilterProxyModel as:
ASSERT: "cm" in file itemviews/qsortfilterproxymodel.cpp line 935.
Now, it seems like a bug. But it is terrible in reproduction. It only happens some times. And I don't get any documentation for this assert. Can anyone tell me what this error signifies?

Created bug for the same. Perhaps need to write some minimum working code to recreate it too.