The version/expiration behavior of Liferay is really tricky and by far too convoluted.
Let's say, you have a webcontent:
v1: Expires March
v2: Expires February, 1st
Now it becomes February and v2 expires. But suddenly the older version v1 is shown since it only expires in March. I had opened a ticket about this behavior at Liferay a while ago and it was explained to me that this is a feature. I hate it, but it is as it is.
The only thing you can do: Expire all old versions of the article through the article history menu.
