When I am in text editing mode and double-click the glyph to the left of the cursor then the glyph to the right of the cursor is opened for editing, not the one I double-clicked. This error does not occur for glyphs further to the left or right.
Btw, it would be great if double-clicking a glyph in the preview pane always opened this glyph for editing (instead of placing the cursor there when the tetxt tool is active).
I have experienced this phenomenon a few times as well, but cannot really reproduce it reliably. What I have found is that repeating the double click in the same position will open the desired glyph eventually.
Are you on a non-Retina screen?
Had some fun playing around trying to understand this. I also get cases when it works.
So, the surprisingly simple and logical answer is: If you double-click into the left half of a glyph then the desired glyph will open for editing, otherwise the glyph to the right (because the cursor jumps to that glyph just before the click gets double.
I was wrong saying that the error does not occur for glyphs further to the left or right. It is independent of the cursor position before the double click.
Nevertheless, it woud be good if this was fixed.
Fixed it. Thanks for figuring it out.
I can’t believe this issue finally got fixed! It’s been around so long that I think I’m going to miss it when it’s gone. 
Incidentally, I’m still getting that error with the newest version.