I don't know if this is a feature request or a bug:  but I get the Event List set the way I want it, undocked and on a separate screen.   If I have occasion to close that window to work on other things, when it reopens it is docked again, right where I do NOT want it.   It is so hard to have the dock/undock status and window location be remembered?    
 

Does LOCKING the screenset help?

When the view is closed, there is nothing for SONAR to remember. It is usually more efficient to leave views open in the X Series. Screensets may help instead of closing views.

Locking the screenset does not help.   Leaving the windows open does, but it's not a great solution: I want visual focus not visual clutter.     If i'm in PRV, that's where my eyes want to stay ... having the bright and big event list still open is distracting, especially because it keeps moving as I change location in the file. 

Minimizing the window will reduce clutter and still leave the window open.

After undocking have you tried a save i.e. Ctrl-S I found this helps in Sonar Platinum in maintaining the undocked status of the Events list for the current screen set.

Yeah, it is the same in X3. A Floating Event List (with a dummy MIDI track) will even persist when saved as a project template.