Ok, love the speed and the browser rendering for the new Edge. I hate the text interaction. This applies to mouse usage on a page, and both mouse and keyboard inside a single and multiline textbox.
The current interaction is not windows standard, and needs to be fixed. A couple of examples.
1) Text like "ABC:123". If this is either on the page or in a text box, if you double click on 123, it highlights ABC:123 (doesn't in this rich text box). It is like certain characters that are considered word breaks in windows are not in cromium
2) After selecting any text in a text box (word, line, all, etc), you cannot click in the selected text and have it unselected. You have to click outside the selection.
3) Pasting in the middle of a large block of text in a large multiline text box will move the text to an unexpected location
It appears that it may depend on the context of the page and they style as you pointed out that it wasn't exhibiting that behavior in a Rich Text format. I will relay your concerns to the product team.