No objections to the registers window when it is docked. But if it is not yet activated and I open it, then after a paste there is a problem. I am unable to close it quickly because the focus went to an editpane. So I suggest one of the following:
1. Don't transfer the focus to an editpane if the registers window is in floating state.
2. Transfer, but close also.
3. A more sophisticated, configurable behaviour.
Simplest to do is 1 which would resemble the behaviour before last changes to this window, for fr #3437779.