U1 login window opens behind pay-ui window

I don't think that the log message is that relevant, since qtmir never supported foreign windows.
This looks like a mir/qtmir/unity8 issue in handling trusted sessions (unless something has changed in pay-service?).
Tentatively assigning to qtmir for investigation.

I also reproduced the issue. Indeed I suspect that Selene is right and that the U1 login window is opening, but behind the "Loading" prompt. Attaching the logs from online-accounts-service; despite the warnings, which are "normal" in this situation, the U1 login seems to be successfully loaded.

I've been bisecting the rc-proposed images to find where the bug was introduced (arbitrarily assuming that this is a 100% reproducible issue):
Working images: 435,440,442; failing images: 445,443

So, it seems that the bug was introduced in image 443, which carries these changes:
http://people.canonical.com/~lzemczak/landing-team/ubuntu-touch/rc-proposed/ubuntu/mako/443.commitlog

The best candidates for investigation are qtmir and unity8:
======
  * Move prompt surfaces from MirSurface to Application and emit
    firstChanged signal
======

Adding unity8 too.

This bug was fixed in the package unity8 - 8.12+16.10.20160617-0ubuntu1

---------------
unity8 (8.12+16.10.20160617-0ubuntu1) yakkety; urgency=medium

  [ Michael Terry ]
  * Do not create Label/Icon if we don't need it
  * Fix Z-ordering of prompt surfaces (LP: #1586219)
  * Drop bottom edge tutorials completely and small fixes for other
    edges. (LP: #1565103)
  * Redo visuals for greeter prompt box. (LP: #1435923)
  * Make tutorial qmltests more robust. (LP: #1590810)
  * Stop showing an extra lockscreen in desktop unity8 sessions. (LP:
    #1582987)

  [ Albert Astals Cid ]
  * Improve dash plugin mock
  * Stabilize PreviewExpandableTest::test_all_widgets_height
  * Workaround QTBUG-53460
  * Split artShape code for cardTool card and regular card
  * Simplify the code since fixedArtSize code is mandatory for regular
    cards
  * Desktop stage: Support rotatesWindowContents (LP: #1547481)
  * Turn if if else into if elseif else
  * Fix leaks in QInputDeviceManagerPrivate::addDevice
  * Do not call |= on uninitialized sigterm.sa_flags
  * initialize udevMonitor
  * Make notifier and notifierFd function local variables
  * Fix crash if a component that is not an Item is given to
    sectionDelegate
  * Tests: Do not use dynamic_cast if we're not going to test it anyway
  * Minor coverity fixes
  * Fix warning about anchors.fill in ProportionalShape (LP: #1590963)
  * Make wait in cleanup() wait for snapTo animation to have finished

  [ Alexandros Frantzis ]
  * Improve the way notifications interact with power management (LP:
    #1570922)

  [ Andrea Cimitan ]
  * Correctly refresh cardcreator cache on artshapestyle changes (LP:
    #1588335)
  * Same tweaks we have for click scope now for libertine
  * add a timer to pull to refresh to work on small windows (LP:
    #1589060)

  [ Daniel d'Andrada ]
  * Clean up debug leftovers
  * Ensure mouse and window movement are pixel-aligned (LP: #1510382)
  * Fix SpreadDelegate rotation animations
  * No point in version-controlling files that are automatically
    generated
  * Center cursor on screen when it's first shown
  * Custom cursor name just have to start with "custom"
  * Work around AnimatedSprite infinite loop bug (LP: #1588929)

  [ Josh Arenson ]
  * Disable showDash when it is already shown. (LP: #1506708)
  * Add a timestamp to the dash log (LP: #1580074)
  * Add timestamp to unity8 log (LP: #1498169)

  [ Lukáš Tinkl ]
  * Implement keyboard shortcuts info panel
  * Implement window controls overlay activatable with 3 fingers tap
    (LP: #1489020)
  * Select correct Chinese input method for OSK in the wizard (LP:
    #1588633)

  [ Michael Zanetti ]
  * Add support for the launcher surface pips displaying the correct
    number of surfaces
  * Add support for the persistent alert state. (LP: #1575147, #1584348,
    #1586621)
  * send a Alt-release event on alt+tab instead of delaying it
    completely and invoking it later (LP: #1565236)

  [ Stephen M. Webb ]
  * added a new upstart $SESSION for unity8-desktop-session (LP:
    #1376715)

 -- Michael Terry <email address hidden> Fri, 17 Jun 2016 01:22:57 +0000