On my computer, when the cursor is in the "Add Reply" box, "page down" works normal the first time but after that "page up" and "page down" do odd things with shifting the page left and right, adding blue margin on the right, and not recovering all the way back to center until I close out the "add reply" box. I try to remember to not use "page up" and "page down" while cursor is in "add reply" box.
Another minor issue: when using "reply with quote" some replies from other people get confused with their added text in the same box as the quote, because apparently the cursor does not default to outside the quote box. When I use "reply with quote" I often have to use "source code" option to get my reply outside of the box with the quote. Some folks use a different text color to differentiate their comments added to a quote.
These are fairly minor issues and I can work around them. Just wondered if others noticed these quirks.