Before seeing this post, I just used Media Editor in 13.0.115, and had no problem.
I found an MP3 track in my collection, an ancient vinyl rip, with very low audio. It was beyond the range of Replay Gain to fix dynamically.
So for a quick fix I opened the MP3 in Media Editor using the same steps in the bug report. I normalized the track, then resaved as MP3 VBR-Extreme. No problems.
Side comment: Unless I'm missing an option, I wish Media Editor could smoothly handle in-place editing of a track. It should recognize that I might want to save the edited track back to the original location and name and format. Instead, it defaulted to somewhere on a different drive and a different media file type. It took some clicking to get back to where the file lives, give it the correct original name, and switch to saving in the original MP3 format.
I realize sometimes the opposite is desired: new name, new location, maybe new format. But a huge advantage of MC having an editor is quick fixes (trimming talk from the front of a live recording track, for instance) and in this situation it would be wonderful to have MC understand the notion of editing the track in-place.
(I do my main vinyl ripping, restoration and editing using Sony Sound Forge.)