New Page Dialog "too low"

Am running 10.3 on tomcat8 with Debian packages… I noticed something today I don’t understand, and can’t think of any changes to anything except new pages added.

I tried to add a link to a page to an undefined page, then go back to click on it to create it. The new page dialog did display, but very low on the page so that the action buttons could not be accessed. Scrolling the page didn’t help, the dialog didn’t move. Tried in Chrome and Firefox with same result.

Attached a screenshot with the example. If I just use the normal “create” button to add a page, I get the creation page fine, so I can work around.
Is there something that controls the placement of that dialog?
Thanks in advance.