I foolishly updated TeXShop recently and I now have the following problem.
Previously, I could highlight text in the editor with the cursor and start typing to overwrite it. Now if I highlight some text to replace "abc" and I start typing something that requires holding shift down, such as "$def...", I end up with "$abc$def...". In other words, the highlighted text is enclosed with $...$ and then the rest of the text is inserted directly afterwards.
How can I get back to the previous setting of simply overwriting the highlighted text?