This was the hardest bug I've ever fixed.
Our custom editable combobox is really hard to maintain regarding input events.
Let's hope this is fixed now.

After some testing in trunk we should backport this to the stable bugfix branch so reporters please test this thoroughly.
The fix consists of two parts.

The first one is to replace the completer window type from popup to tooltip. This was done to avoid stealing the keyboard input from the combobox's lineedit. So far we where relaying key press/release events to the line edit but this is not enough for using input methods (see QInputContext).

The first part enabled using input methods after showing the popup but for the first time we show the popup. This was because somehow showing the popup would mess up the input context of the widget. Work around this with a second fix: create a new input context for the combobox each time the popup is show.