Steps to regenerate
If I type this sentence into the editor:
The quick brown fox jumps over the lazy dag.
And then click the spell check button, it catches the misspelled "dag" and suggests "dig" as the top suggestion. The correct "dog" is further down the list, so I select it and hit replace. It instead replaces "dag" with "dig". In all cases, it simply chooses the top suggestion instead of the one I've selected.