Membership expires field not updating

I have been using the membership plug in since January and am just now getting familiar with all of it's various features.

I have just noticed that the expires field is not updating properly. I have many members who are set up for monthly recurring billing through 2CheckOut, but their expires dates are not updated with subsequent payments. It appears as though the original expires date from the first time they signed up stays in that field, but is not updated each time they are successfully re-billed.

I have verified the membership tables and all is well.

How can I correct this?