I noticed this a while ago since I am using Domino V10 but now I did some investigation. For some reason the toolbar button to add a new image from a file was missing. This is the action that presents you a dialog where you could choose a file to upload.
This is how the full toolbar looks like on Domino 9 and before:
And this is what I got when running the same page on V10:
The button is no more. If you also experienced this behavior you probably also used an extra plugin called „autogrow“. I added this for some reason to the control. I guess I did that because in 9 or older the editor did not grow automatically while typing and when the content grew over the visible area. I that case you got a scrollbar which I personally find annoying. This plugin solved this issue - but caused the other one.
As Ben Langhinrichs pointed out in the comments, the spell checker is also affected. Thanks for the hint!
If you run your application in a mixed environment with 9 and 10 servers you should control the usage of this plugin based on the version of the server. The simplest way to do this is using the @Version() formula with the loaded property of the dojo attribute: