Description:
I have a table in a LibreOffice Calc document, which calculates the final grade and some statistics for student projects of a course I give. Besides the points, there is a column for comments, in which I note down my observations of the work of the individual groups. Each cell in the column holds typically a multi-line text, where the first character of each line is either '+' (positive), '-' (negative), or '*' (neutral) followed by a short note text. I enter this text live during the project presentation so that the current cell is in mode editing for several minutes. This has been working fine for me since 2015 and LibreOffice Calc would run reliably without crashes as far as I can remember.

Since LibreOffice 6.2.0.3, I am observing frequent crashes (approx. 3 to 5 times per 90 minute session) while editing these multi-line comments. The comment cells have no particular assigned cell format. However, it may be relevant for the bug to trigger, that I copy the multi-line comment using a formula to other lines of the comment column using a cell formula, e.g., "=G6". The error message preceding the crash is always the same "Fatal Error: Invalid child index". After confirming it, LibreOffice Calc crashes and needs to be restarted. The file recovery succeeded so far each time, however entered comments were losts: at least the one I was actively editing and sometimes also previously edited comments (depending on the last moment of saving the document).

So far, I was able to reproduce this error on LibreOffice 6.2.0.3 as well as 6.2.2.2, which were always running on macOS High Sierra 10.13.16 of a MacBook Pro 15 inch 2017 model.

Steps to Reproduce:
1. Repeatedly edit multi-line comments, where the lines start with '+', '-', or '*'
2. Have these comments copied to other cells using a cell formula, e.g., "=G6"
3. Don't assign any particular cell format such as "Text"

Actual Results:
Application crashes while editing multi-line comments containing characters, which may be treated as mathematical operators

Expected Results:
Application does not crash due to editing multi-line comments containing characters, which may be treated as mathematical operators


Reproducible: Always


User Profile Reset: No



Additional Info:
Version: 6.2.2.2
Build-ID: 2b840030fec2aae0fd2658d8d4f9548af4e3518d
CPU-Threads: 8; BS: Mac OS X 10.13.6; UI-Render: Standard; VCL: osx; 
Gebietsschema: de-CH (de_CH.UTF-8); UI-Sprache: de-DE
Calc: threaded