That seems to be a bug. I had a post become a completely different one, while typing out a comment, once. There’s also the front page sometimes refreshing in annoying ways, or showing posts from clearly different sort methods. Or posts appearing from other communities, on a community page! All of these seem to go away with a refresh, tho.

This is all new, very complex, and put together by volunteers. I don’t know if you are familiar with FOSS software development, but us users can help by reporting on issues, when we run into them.

Here is the github of the Lemmy project