Moved to Win10 and Edge a few weeks back, and last night went to post a 'reply' to a post on the forum. I did a 'Preview' first to check the formatting, and noticed the preview pane was only one line deep, with scroll arrows on the right-hand side.
Did a bit of experimenting this morning, and noticed that in IE, the preview pane grows with the size of the post, but does not do so in Edge.
Looks like a minor incompatibility between Edge and the forum s/w.
Del