Hi Mike,
There are a few things I would check.
For the blank popup, have you made sure the ActiveRecordID is set when the popup loads? I'm wondering is there's an issue with how the recordID is being loaded when the screen loads. Using the stock CRM_NewActivity screen as an example, there are conditional statements that check for values and loads the screen according to those values. As an example, some fields are set differently depending on if its an activity vs. a log call vs. a task. My advice would be to try to find out what being loaded when the screen loads and where those values are coming from. Perhaps a value is not being set and should be.
I'd also find out when the screen was last updated and by who. Perhaps a change was made and not communicated.
As for the tab header, this is set by an action result called EditCustomerName. The main value for that action result is retrieved from the Customer.FullName field. All of these actions can be found on the "OnLoadAppearance..." button in the Address Info section of the Edit Customer screen (around action #21). If this value is staying the same. then from the sounds of it, I think there is an issue with having the correct ActiveRecordID set when closing the popup.
Unfortunately, I can only do so much through the forums. I am basing all of my info off of a stock screen design. If your screen is heavily customized, I'd recommend having a consultant take a look at it with you to properly diagnose where the issue lies.
Hope this helps,
Adam