Chinese qml input broken on iOS

Since the last iOS update (iOS 13.1.2), the qml text input don't behave properly when using Chinese input: on the first edit, it is possible to add text, but after the input has been accepted, it becomes impossible to select it again, and no other text input work either.

To reproduce:

• Create a qml app containing a single TextField or TextInput, or use any qml examples that has a qml text input.
• Enter some Chinese text in the input, using the pinyin or zhuyin input method (not the handwriting input method, this one works).
• Accept the input
• Try to reselect the input and enter text.  This doesn't work.  Also, pressing anywhere on the screen brings the virtual keyboard up.

(Note that there is also a font rendering bug with a workaround on iOS, this is an other problem).

I tried with older versions of Qt: 5.12.4, 5.12.3 and 5.12.2, they all have the same bug.