Archived posts only appear when the admin panel has been opened in the same browser

Hiya:

I looked through the forum, but didn't see this issue listed elsewhere. If it has and I've missed it, please accept my apologies.
Here's the thing:
When I look through my archives, the headers will appear in the summary page, but if I click on the link, I get a message saying that whatever I was looking for isn't there. Okay, troubling, but I'm migrating from Typepad, so I'm expecting weirdness.
But, if I also open the admin panel in the same browser (different tab), the archived posts appear just fine. No problems at all.

I've tried this with both Safari and Firefox and it works the same, regardless of which I’m using at the moment. Also, if I close the admin panel, the archived posts still appear just fine.

Has anyone else seen this behavior?

Thanks.

Mark