Text input expands incorrectly when moving cursor

When composing text and then reposition the cursor with the mouse in the text input field the virtual keyboard starts to send additional input to the window although no text was composed.

Steps to reproduce:
1) QT_IM_MODULE=qtvirtualkeyboard kwrite
2) click into kwrite text field, keyboard opens
3) Compose Test
4) commit the state by e.g. passing focus to another window
5) Click into text "Test"
6) "Test" expands to something like " TeTeststTeTestst"

From my investigation I think this is caused by the virtual keyboard not adding an attribute with QInputMethodEvent::Cursor to the QInputMethodEvent with the preedit text.

I attached two screenshots showing the composing in point 3 (virt-keyboard-stage1.png) and point 6 (virt-keyboard-stage2.png).

The problem is not specific to kwrite, I could also reproduce it with all other applications I tried.