@Eugene233 I'm not sure how to do that, sorry.

In T183127#3844375, @TheDJ wrote:

No, this is not possible without using an empty cell. Hiding the cell changes the structure of the table and thus breaks the table.
You should rework your content not to require something like that as there is no sustainable way to do what you want with wikicode + html + css.

Closing as invalid as this is not a Wikimedia/Mediawiki bug or feature request.

In T183122#3844384, @TheDJ wrote:

Ehm, doesn't this just depend on how you scrolled ? 1px of the commandbar + 1px of the border makes 2px, but if they happen to overlap because of the scroll offset than it's logically appears like one, because the line of the table is hidden behind the commandbar (just like all the other content that is above the table).

This doesn't seem like a bug to me and I have no idea why you would expect there to be only a 1px line...

In T183124#3844450, @Deskana wrote:

As was suggested in T178005#3679804, this is likely a browser glitch which we can't do anything about.

As an aside, I tested in Safari, Chrome, and Firefox on Mac OS, and Internet Explorer 11, Chrome, and Firefox on Windows 7, and could not reproduce this issue in any of those browsers.

If I update to the newest version, will my saved settings still be intact or will I have to start over?

Perhaps, I am not exactly sure.
The bot mode, probably.