It is related to a kernel bug.
Don't know if you have the ability to upgrade kernels on EC2, but this bug can be worked around by installing one of the latest Ubuntu Mainline kernels.
You need at least: linux-image-3.15.0-031500rc2
Reference: http://www.deinon.com/wiki/doku.php?id=linux:ubuntu
It is related to a kernel bug.
Don't know if you have the ability to upgrade kernels on EC2, but this bug can be worked around by installing one of the latest Ubuntu Mainline kernels.
You need at least: linux-image- 3.15.0- 031500rc2
Reference: http:// www.deinon. com/wiki/ doku.php? id=linux: ubuntu