I'm pretty sure the Show/Hide tool bars has nothing to do with it. It more has to do with the context of the layout you are going to (LayA) and what record you are landing on since that record determines what is in the portal. Can you tell us more about the relationship between LayA's table occurrence and the portal and more about the portal such as if there are portal filters, etc.?
It is very vanilla, I have a parent linked to childern records. The parent is note category and the children are notes in that category, simple one file link. There are no filters, nothing else. If I use New Window with Show/hide Toolbars [Lock/Hide] in a script I can only see one parent record and its children lines. A straight go to Layout and I can scroll through all of the parent records and their children. I just want to see all of my notes from any FM layout, notes accessed via a button.
Have you tried using Adjust window (resize to fit) when you change layouts?
Since the layout is in form view, the only way to scroll through the found set of records is by having the status area either unlocked when hidden or by having it visible. I dont think the lock status matters when visible, but it most certainly does when its hidden.
Locking the status area when its hidden (on windows anyway) intentionally prevents scrolling through the parent records but only if the layout is being viewed in "form view", which is what you stated. Its been this way for quite some time.
Of course, this assumes that when changing back to LayA via script you still have more than one record in the found set too.