Sol, here's an example of how the highlight-capture problem works: 
I tried to capture everything from "In this city" to and through "price of his bones." The capture was extended to the beginning of the paragraph, and to the space after 'bone.'. Whether the problem lies in Windows, IE, or your web page, it prevents me from writing the comment I want on the text to which the comment appertains.
Maybe the surest solution would be to allow comments to overlap. That would complicate both the capture and selection mechanism, but (especially with X-line format) I can see solutions.
This is a regular source of frustration to me as a reviewer. Nor can it help the writer reviewed that I have to explain in the comment that the comment applies to text other than than highlighted.
Postscript: The problem occurs even if I only extend the capture to the end of the paragraph. I have to stop it after the penultimate word, whereup on the capture is extended to the last word--but not to the period ending the sentence.
This is a recurring pain in tender places.