Windows 7 misses keystrokes from internal keyboard after hibernation on Acer Aspire 5820

After waking my computer (Acer Aspire with the factory default Windows 7 install and divers, Windows update running) from hibernation, it is a pain to type, since on average 5-10 keypresses are missing per 100 presses, using the laptop's keyboard.

Steps to reproduce:

1. Power off


2. Power on, wait for system to become usable


3. 
   

   Open Notepad, for five times enter 10x the same character. This gives a similar pattern of 50 characters total:

   
   

   
   

   xxxxxxxxxxyyyyyyyyyyaaaaaaaaaassssssssssdddddddddd

   
   

   
   


4. 
   

   Optionally repeat. Everything is fine this far.

   
   


5. Hibernate


6. Power on and resume


7. Repeat steps 3-4. This time approximately 3-5 character will be missing from each 50 characters

What I ruled out:

• putting to Sleep or just Locking and resuming from there does not cause problem


• battery / AC usage does not matter


• Internet connection does not matter


• running processes seem to be the same before and after hibernation


• keypress speed doesn't really matter. For the test I use a nominal 3-5 strokes/second beat.


• plugging in an external USB keyboard works fine, but the built-in one still misbehaves

What could be the problem? How could I diagnose if the keypresses arrive in, but get swallowed at some point? (maybe some nasty keyboard handler hook misbehaves?).

Pushing the PowerSmart button and toggling to power saving state fixes the problem. Also, toggling it again back to the original state keeps it fixed. So this may be a fine workaround, but is not a conforming solution.