use _build_filters function instead of specifying request params manuall...

...y
According to the EC2 API reference, the way filters are built is common for all resources.

<quote>
Filter.n.Name
The name of a filter. For more information about supported filter names, see the Supported Filters section.
</quote>

<quote>
Filter.n.Value.m
A value for the filter. For more information about supported values for each filter, see the Supported Filters section.
</quote>

from: http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-DescribeVolumes.html

So its weird that it worked before, or did it work at all ?
This looks like a bug.