Weird overlapping text on TMemo

[Trenatos]

I have an application that uses TMemo with Carbon. (Lazarus 1.9.0, FPC 3.1.1)

It's a development tool for local webservers, so deals with lots of output text.

Both users and I have found that often when the application adds text to the tmemo (AddText()), it'll overlap rows or sections of text, but if you resize the tmemo it goes back to normal again.

I've attached screenshots of the issue and after resizing.

No idea what's causing it or how to fix it  :/