On two of my forums (version 1.1.11), even when I have the "not collapsible" option ticked in the block edit:
the block remains collapsible using the little clickable square above the block:

I just assumed that was the way it was until I discovered that on my most active forum, also version 1.1.11, the block actually becomes non collapsible when I tic the box in the block edit.
I have checked everything I can think of that might be different between the two but can't find a thing.
Both of these forums have the "not collapsible" box ticked but this one is still collapsible:
http://norcalcarpclub.com/forum/and this one is not:
http://catfished.com/forum/
Edit: Never mind, I finally found it. There's a box in Simple Portal's General Settings entitled "Disable Side Collapsing". I ticked it and now they're all non collapsible. I'm leaving this as is in case anyone else has the same problem.