issue with editing of a single messages with more than 10 lines in riot-web on Linux

[git-minix]

Description

If longer messages (larger than the edit windows) are written with Riot-Web on Debian 9.4 and Mint Linux, the scrolling will not work correctly and sometimes the content of the previous message will be merged into the new message.

Steps to reproduce

• go in a room and write a message like "this is a test - line Leave room button #1" with 15 lines
• do not use CR after each line, use SHIFT CR or copy the message via Copy&Paste form a text file
• use the cursor keys to move from the top to the bottom in the edit window
• try to edit the message in different lines

The editing of such messages does not work reliable.

Version information

Testet with Debian 9.4 and the riot-web package 0.13.5
Testted witt Linux Mint 18.3 Sylvia and the riot-web package 0.13.5

from: deb https://riot.im/packages/debian/ stretch main

• Platform: desktop
• OS: Debian 9.4 and Linux Mint 18.3 Sylvia
• Version: 0.13.5

[lampholder]

I wasn't able to reproduce this on 0.13.5 running on my ubuntu machine, though I think under different circumstances the RTE can get into a very confused (but difficult to reliably reproduce) state.

[ara4n]

i've seen this a few times under OSX.

[ara4n]

fixed by matrix-org/matrix-react-sdk#1890, hopefully