Formatting tools split the screen

This could be a good thing, but it isn’t!

I’m typing along on any page or blog post and should I scroll down, after a while, the bottom two rows of the formatting tools moves into the middle of the screen, covering part of what I’ve typed. You would think for a long post this would be helpful, but I can’t link text to someplace else because the link icon doesn’t show. I scroll back to the top of the page, and the formatting tools still show only the bottom two rows. There is no scroll bar alongside the tools, so I’m sunk. To see all four rows, I have to update the page, but there is no guarantee that this won’t happen again, esp. if the link needs to be made at the bottom of a long page. This has been going on with previous versions of WP, also when running Windows 7 and now 10. I think I wouldn’t mind the split screen if ALL of the formatting rows would move as a page lengthens, but they don’t. Seems like a verified bug that I hope can be fixed. Thank you.