I wasn't able to reproduce the issue on a default kbin setup with KES either on off. The "always expand post bodies" feature of KES only applies to bodies, but I could extend it to support comments as well so that they auto-expand. What I didn't observe was any situations where the expansion bar obscures the text. Do you have a screenshot of that?
Are you running a custom theme?
Thanks for looking into this. I've been meaning to audit this mod, but was a bit busy this week. In light of this report, this seems like as good a time as any.
Unfortunately, the mod is no longer maintained by the original author, so I'll have to inherit it and refactor it. I feel it is overengineered for what it attempts to do, so it should be streamlined and the aforementioned issues fixed. I am also aware of the issue that the mod fails to unset itself properly when turned off. I am really not satisfied with its current functionality.
Root cause analysis and solutions are described in a subsequent comment