horrible change in alt-backtick behaviour

In the last two weeks or so, an update has changed the behaviour of alt-backtick in a really unpleasant way. Suppose I open three instances of Emacs, opening different files in them and resizing them so that they are easily visually distinguishable. Suppose the currently focussed window is A, and the other two are B and C.

Then, if I hold down Alt and press backtick (`), I very briefly see in the thumbnail view:

   [B] A
   C

... where [] indicates the focussed window. Then, with fractions of a second, this is replaced with:

   [A] B
   C

... and if I release Alt, then I'm returned to A again. Previously, a single press of Alt-` would always switch to the next window, so this change is really disruptive. Also, the visible reordering of the thumbnails is distracting and confusing. The new behaviour is also inconsistent - if I do a quick Alt-`, then B *will* be focussed, but if I hold down Alt too long, A will be remain focussed.

This is distinct issue from that described in bug #987156, although the nasty change in behaviour I'm describing here is mentioned in a comment on that bug: https://bugs.launchpad.net/unity/+bug/987156/comments/15

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity 5.14.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-29.46-generic-pae 3.2.24
Uname: Linux 3.2.0-29-generic-pae i686
NonfreeKernelModules: fglrx
ApportVersion: 2.0.1-0ubuntu12
Architecture: i386
CompizPlugins: [core,bailer,detection,composite,opengl,compiztoolbox,decor,resize,vpswitch,imgpng,mousepoll,unitymtgrabhandles,gnomecompat,snap,place,regex,move,grid,wall,session,animation,workarounds,fade,expo,ezoom,scale,unityshell]
Date: Wed Aug 15 09:41:17 2012
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
SourcePackage: unity
UpgradeStatus: Upgraded to precise on 2012-04-29 (107 days ago)