Thunderbolt display: devices not discovered after using Mini DisplayPort–to–VGA adapter

I have an interested problem related to using my MacBook Air in clamshell (closed) mode, connected to a Thunderbolt display. The problem appears to be related to moving my MacBook air between my office and my home.

At the office, I use the MacBook Air with an external VGA display, connected via the Mini DisplayPort–to–VGA adapter. At home, I use the MacBook Air together with a Thunderbolt display. An Apple USB keyboard is also connected to the display.

Mini DisplayPort–to–VGA adapter implicated

The following sequence of events causes the problem to occur:

1. Use the MacBook air (open) together with a VGA display, connected via a Mini DisplayPort–to–VGA adapter (depicted at right);
2. Put the MacBook Air to sleep by closing the lid, and disconnect the Mini DisplayPort–to–VGA adapter (I am not sure if the order of these two steps is significant—I usually perform them almost simultaneously when packing up my MacBook Air and getting ready to leave the office); and
3. With the MacBook Air still closed, connect it to a Thunderbolt display with a connected USB keyboard.

At this point, I would expect to be able to wake up the MacBook Air by tapping on the space bar of the keyboard. However, what I have observed is that this does not wake the MacBook Air.

I can wake the MacBook however by moving or clicking a Bluetooth mouse that is paired with the MacBook Air.

At this point, although the MacBook Air is awake, and the display is working, the USB keyboard connected to the display still does not work. This is the problem, in a nutshell.

Unplugging the USB keyboard from the display, and plugging it back in causes the MacBook Air properly to identify the keyboard.

I used Apple System Profiler to save a list of identified devices at two points in time:

1. Immediately after waking the MacBook Air by moving the Bluetooth mouse (at which point the USB keyboard was not working); and
2. After unplugging and plugging in again the USB keyboard (at which point the USB keyboard worked fine).

Many devices are enumerated in the second list that are missing from the first. For example:

Keyboard Hub@fe110000 <class IOUSBHubDevice, id 0x1000378ef, !registered, !matched, inactive, busy 3 (37993 ms), retain 6>

AppleUSBHub <class AppleUSBHub, id 0x1000378f2, !registered, !matched, inactive, busy 1 (37987 ms), retain 6>

IOUSBInterface@0 <class IOUSBInterface, id 0x1000378f4, !registered, !matched, inactive, busy 1 (37986 ms), retain 6>

Keyboard Hub@fe110000 <class IOUSBHubDevice, id 0x1000378f6, registered, matched, active, busy 0 (7 ms), retain 10>

AppleUSBHub <class AppleUSBHub, id 0x1000378f9, registered, matched, active, busy 0 (1 ms), retain 9>

IOUSBInterface@0 <class IOUSBInterface, id 0x1000378fb, !registered, !matched, active, busy 0, retain 7>

Apple Keyboard@fe112000 <class IOUSBDevice, id 0x1000378fd, registered, matched, active, busy 0 (112 ms), retain 11>

and many child devices…

Using the Mini DisplayPort–to–VGA adapter appears to be a necessary step to causing this problem to occur. If I merely disconnect the MacBook Air from the display, let it go to sleep, and then reconnect it again, the USB keyboard will work immediately and can be used to wake the computer from sleep.

Some devices are discovered even when the computer is in sleep mode. This is how it should work.

The problem appears to be that when a Mini DisplayPort–to–VGA adapter has been used since the last time the computer was connected to a Thunderbolt display, the MacBook air does not discover devices completely when it is again connected to the Thunderbolt display while in sleep mode.

Can anyone else reproduce this problem?