debian sid, XFCE, recent upgrade, 2 external monitors, resolution of one not remembered

[Zenaan Harkness <zen@freedbms.net>]

I have a laptop with 2 external monitors, both WUXGA - 1920x1200.
I recently upgraded my sid installation.
I use startx to start my XFCE session.

After the upgrade, when I startx, XFCE does not remember the
resolution and layout of my monitors - it gets the right hand monitor
resolution correct, but the left defaults to a significantly lower
resolution (matching the laptops 1366x768 it seems), and the two
screens both have the same origin point (as viewed with arandr
utility).

Any ideas what might have changed, to cause XFCE to stop remembering
the most recent .screenlayout/blah screen layout?

TIA
Zenaan