Regarding the lock/unlock toolbutton. The issue is that the checkstate is inconsistent. Sometimes it is checked when unlocked, other times it is checked when locked. It depends upon the combination of actions that you take. I think it is actually unnecessary for the toolbutton to be checkable. What matters is that the user can see whether the item is locked/unlocked, and that is the case due to the change in the icon and the enabling/disabling of the delete button.

I see what you mean about adding the existing clipboard item on startup. I didn't consider that. It's actually a really good idea, so I think you should leave it as it is.

It is possible to display a menu and the virtual keyboard at the same time. I have implemented this in my own applications. The menu shifts up when the virtual keyboard is displayed, like this: