Blurred and fade font color during editing

[Blazej]

I’ve noticed it’s happening for some time. I’m opening larger file. Text is sharp, as soon as I start editing text starts flickering between blurred and faded slightly. It stops when I want to record this behaviour. Has anyone noticed it?

I’m using ST 4200 on 26.3.1 (a) (25D771280a)

[aklaver]

This is going to need more information:

OS and version.
Machine memory size.
File size.
What is file e.g html, C source, etc.
What extra packages do you have installed?