Don't ask me how this happens--I just wanted to let you know that the problem was out there. What typically happens is that I download a new module, excited to read its contents, and to my surprise, discover that half the text is hightlighted with different colors, throughout the module, or else, only in parts.
Of course, those of you who use a bright white background on every bookview window, might never notice, as sometimes the highlighting is actually white itself. Try a light-gray background, however, and you will see it appear (see the screenshot below). This makes the text much more illegible. Other times the highlighting appears in a different color.
Of course, TW is supposed to allow the user to use different colored backgrounds, perhaps to make it easier to manage windows, or for those who work a dimly-lit room, and don't want the brightness of all-white windows to interfere with their reading. (Programs for recording studios often give their customers the option of having a darker interface, for just that reason).
Nevertheless, this is all somewhat beside the point, because, regardless of which background options you use for the book view windows, you will notice that the same mysterious highlighting problem occurs, not just with the module text, but in the "about" tab of the "module properties window." (See screenshot below).
I am afraid I have no solution to report, but only the problem. I am hoping that Mr. Josh Bond will give us all the perfect fix, below, in a response to this post, or perhaps even Mr. Stergiou himself. In the meantime, perhaps a temporary work-around would be to "select all" of the text in each chapter of your new module--before preparing it for distribution--then, to choose "none" among the highlighting options on the color palette, while the text is still selected, and then repeat the process with each subsequent chapter (don't forget the title page and introductory material, too).
Meanwhile, maybe Mr. Stergiou will modify TW so that it will automatically remove such hidden highlighting, before allowing the user to create and distribute the module.
God bless you all for your hard work and you willingness to share the modules.