Is is selecting the surface that was originally created and only appear to be multiple surfaces due to being interrupted due to later features? Try Next, Previous, or Pick From List to get the sub-element.

Since you did not mention what else you might know, check Seed and Bound: http://support.ptc.com/help/creo/creo_pma/usascii/...

I used the seed and boundary, in the picture is just for explanation. In reality I used seed and boundary to select all the inner surfaces.
Then this outer surface and 1 more also were included somehow...

It was 1 surface and indeed later obstructed by the wall. But in all the other CAD programs I have used it never does anything similar.
It should just select a surface till its edges and not every other surface parallel & at the same height to it as well...

In the pressure interface in Simulate I don't have an option to choose a subpart of the selection either.

It did the same with this cylindrical surface.
Though it does it on the left and not on the right, even though the right cylinder also continues on the backside.
What makes it even worse, both left and right cylinders are made with the same sweep feature, so Creo really does some weird stuff...

In CREO surfaces belong to 3 levels: The entire surface set that was created when the feature was created; the original surface set before any other features interrupt it; the individual surface patch. It's not picking every other surface - it's picking the one surface.

Maybe there is a bug in this version of the software, something that happens. I never noticed it in the nearly 20 years of using Creo/Pro-Engineer, but I didn't use all the analysis packages that were grafted on.

Contact PTC support or the VAR, depending on the support contract, and show them that Seed and Bound is picking surface elements outside the boundary. They may want a simplified model that shows the defect in order to understand how this is happening.

Thank you for trying to help at least.
I will contact support, was just hoping for a simple solution like switching from 'original surface' to 'individual patch'.

That's why I suggested "Next, Previous, or Pick From List" to get the sub-element.

How do I do that? When selecting the surface I don't get an option to do next, previous and pick from list?

Edit: already found out how, by holding the right mouse button

But it doesn't give me the option to select just the interrupted surface patch / the surface bounded by its newest edges. It has nothing to do with Simulate cause I am trying it in Parametric.

Contact PTC support or the VAR, depending on the support contract, and show them that Seed and Bound is picking surface elements outside the boundary. They may want a simplified model that shows the defect in order to understand how this is happening.

The solution to this problem is the split surface command under the Model tab -> Editing.
Then one can select the surface and choose which to exclude.
So the next time you select the surface it is selected without the excluded surfaces 🙂