Regression in code-completion triggers

See attached animations that try to get code-completion for the signal signature in connect(ui->treeView->selectionModel(), &QItemSelectionModel::...

These animations were taken with the Clang Code Model disabled. However, similar behaviour is observed when the Clang Code Model is enabled.

Qt Creator 4.15.1 behaviour (Good)

• After inputting "connect(ui->treeView->selectionModel(), " typing "&QItem" triggers code-completion. We can input "&QItemSelectionModel" easily.
• Typing "::" triggers code-completion for the list of signals.

Qt Creator 6.0.2 behaviour (Bad)

• After inputting "connect(ui->treeView->selectionModel(), " typing "&QItem" does nothing. We must type every character of "&QItemSelectionModel" manually.
• Typing "::" triggers code-completion for the list of signals.

After the list of signals is shown, the "function overload combobox" for connect() disappears. We now erase the class name; as long as the "function overload combobox" remains hidden, we can now type "&QItem" to trigger code-completion for "&QItemSelectionModel".

However, if we erase the ',' then everything is lost again. Typing ',' brings back the "function overload combobox" and typing "&QItem" no longer triggers code-completion.

Partial Workaround

After inputting "connect(ui->treeView->selectionModel(), " press [Esc] to dismiss the "function overload combobox". This allows "&QItem" to trigger code-completion again.

Caveat: This workaround cannot be used if FakeVim is enabled because pressing [Esc] kicks the user out of edit mode.