macOS QPlainTextEdit accented characters blocking text selection

If a QPlainTextEdit is used on macOS Mojave and a accented character is typed then QPlainTextEdit blocks user actions like text selection. This behaviour occurs when the accent character is pressed and a user tries to select text, like he wants to abort the writing of a composed character. With Qt 5.11.2, 5.11.3 and 5.12.0 the QPlainTextEdit blocks text selection if the first half of a composed character is written.

Steps to reproduce the issue with the attached project.
1. Make sure you have a German or French keyboard layout configured
1. Write some random text, like "asdfkasklfhkashgkg"
1. Go to a new line
1. Type ´, like you would type á
1. Do not press a!
1. Try to select the random text with the mouse

Result: The text selection on macOS is not possible, but on Windows 10 it works. Other apps like RStudio or the native TextEdit on macOS Mojave don't seam to have that issue.

I did a test on Ubuntu 18.04 LTS and the QPlainTextEdit behaves like expected, i.e. the text selection is possible. Furthermore, if you type a ´ and relocate the cursor to a different line and enter a afterwards the á gets inserted at the cursor position. This behaviour is consistent on Ubuntu and Windows. On macOS this is not possible because of the locked QPlainTextEdit.

Example project: https://github.com/MrMontag/macos-de-keyboard

Forum: https://forum.qt.io/topic/97713/macos-qplaintextedit-accented-characters-blocking-text-selection