Akismet randomly pending comments

I run a multi-user blog, and just within the last week Akismet has begun randomly holding their comments as “pending”, forcing me to approve them. I’ve been using Akismet happily and successfully for years with no settings requiring comments to be approved. All users but me are Author status.

This started with just one comment a week ago but has begun to accelerate such that by today there were 5 or 6 at one time. Nothing has changed except the WP version upgrade now to 3.6.1.

Any clues or ideas how to stop this?

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