Likely because the buttons of the editor are stretching the wrapper element. We used to have that same problem here, and might still to a certain degree.
You should be able to add some CSS to work around it for your specific application.
thanks for your reply 🙂
im a newbie to WordPress, add CSS does that mean edit coding?
Yes, but try using a Webkit browser on your PC or Mac ( Chrome or Safari are Webkit based )
Scale your browser-window down to iPhone size and try to spot at what size things start going wrong -layout wise.
Just before things start going wrong you Right-click at the page where things go wrong and pick the ‘Inspect Element’ option to see the code. It really helps a lot.
Hey shmoo, thanks for the reply
I am using Firefox on Windows. I scaled my browser and the forum cuts half way. After right clicking on ‘Inspect Element’ what do i do next???
View the source, walk through the elements and they should highlight. I can’t tell you what to do from this side of the internet. You have to have a little understanding of HTML + CSS.