I've been able to confirm the same as the OP regarding the different Ubuntu distrubutions as guests. These tests should help ruleout/pinpoint the kernel and modules.
Using the same 12.04 hypervisors for all tests.
Testing different guests I was able to determine.
-Lucid with default kernel is NOT affected.
-Precise with default kernel is affected.
The test...
I tared up each guest kernels and dropped them into the oposing distribution.
Results
-Lucid with Precise Kernel is NOT affected.
-Precise with Lucid Kernel is affected.
Conclusion
12.04 Precise distribution guest is affected regardless of the kernel used.
I've been able to confirm the same as the OP regarding the different Ubuntu distrubutions as guests. These tests should help ruleout/pinpoint the kernel and modules.
Using the same 12.04 hypervisors for all tests.
Testing different guests I was able to determine.
-Lucid with default kernel is NOT affected.
-Precise with default kernel is affected.
The test...
I tared up each guest kernels and dropped them into the oposing distribution.
Results
-Lucid with Precise Kernel is NOT affected.
-Precise with Lucid Kernel is affected.
Conclusion
12.04 Precise distribution guest is affected regardless of the kernel used.