Major cache, cookie or session issue after upgrade to 5.1.5

[DisasterDotCom]

No - I'm not complaining that the first thing they told me was to clear the caches. What is a bit upsetting is that I replied to the request within 15 seconds and they have not replied back yet (since yesterday) except on the vbulletin.com board. But, right now, I care more about solving these problems than complaining about poor support response times.

In between testing I'm enabling the "no-cache" function ("Add No-Cache HTTP Headers").

I do appreciate your responses.

--------------- Added [DATE]1423067894[/DATE] at [TIME]1423067894[/TIME] ---------------

So just to update... I turned debug on in the config file and looked at time stamps (generated BY vbulletin at the bottom of each rendered page):

Initial Post - Current Time: Wed, 04 Feb 2015 11:31:39 -0500
After Comment - Current Time: Wed, 04 Feb 2015 11:31:39 -0500
Click on forum link - Current Time: Wed, 04 Feb 2015 11:31:03 -0500
Hit refresh - Current Time: Wed, 04 Feb 2015 11:33:12 -0500
Click on topic again - Current Time: Wed, 04 Feb 2015 11:31:39 -0500
Click refresh - Current Time: Wed, 04 Feb 2015 11:35:15 -0500

Note that when I click on the forum link I go back in time (even though I've made a new post). I refresh, we come back to the current time.

Then when I click on the topic again, the time stamp matches the initial post time - NOT the time after I made the comment. Once again, I refresh and we come back to the current time and the reply shows.