When I select a word or words within a paragraph and apply Bold on it, either in Author or code modes, it will Underline the selected text.
The same thing will happen if I try to underline a word or multiple words in a paragraph. The selection will underline and will be Bold.
How can I avoid that?
This looks to be much the same as the issue in Format to Bold where I offered to take a look. As I didn't hear from you I assumed you didn't want to take up that offer.
Did I suggest in response to one of your posts that you apply default.css to the topic just to see if it fixed that issue? The default.css has changed with the updates so create a new project and copy the file from that project to this one, then apply just that css.
See www.grainge.org for free RoboHelp and Authoring information.