I am having the same problem. This method works OK in Pro, but only seems to work in Go if the portal has no scroll bar. That said, the GoMaps solution by SeedCode uses this technique successfully using a portal with a scroll bar in Go. I have attempted to copy mimic the GoMaps solution without success. No matter the stacking order and style of objects, a sliding tab control will not hide the objects in a portal with a scroll bar. Ideas?
I believed this process worked well in FileMaker Go 11 but it broke or doesn't work as nicely in FileMaker Go 12.
I had the same problem for some time until I found the answer. Tanner Ellen at SeedCode pointed this out to me.
So what you do is:
In my case I had two portals on tab panel the left that are hidden beneth the sliding main tab panel that covers them up in portrait and reveals in landscape mode.
So, after you have the portals how you want them:
1. set portals to be 1 px wide anchored left and right so it expands when the iPad is rotated. ( there is one portal on each of the two left tabs, these tabs are fixed left and do not slide )
2. then set the left tab panel with the portals on it to 1 px wide anchor left and right so it expands when the iPad is rotated.
3. your main tab panel is just set to anchor right so it slides over revealing the portals that are set below the tab panel.
That's it. It is a little more time consuming when you have to make changes to the hidden portals or tabs, but thank goodness IT WORKS !
I found I had to remember to also set the portal itself to 1 px wide. If you just set the left tab panel to 1 px wide it will hide, but when you open it on the iPad your back where you started with the seeping portal text and buttons.
If there are fields or buttons that are hidden on the left that are not in the portal, and not on a 1 px wide tab panel, they will function through the sliding tab panel. So this is fixed if they sit on a 1 px wide tab panel.