I do not experience this — the Hide when Printing setting is removing the button from portal rows, at least when Previewing the layout.
Suggest that you check that the button is neither grouped with anything, nor touching the edges/borders of the portal row. If that reveals nothing, try deleting the button object, then recreate it on the layout (don't just cut/paste), and be careful when setting the Hide when Printing option that only this button object is selected — with nothing else touched during the selection process.
Also check that the object has no "Sliding" during print setting, as that is a contradictory print instruction (though I haven't tested what result that might cause).
If the problem persists, provide details of your OS and FMP versions, some "bugs" appear only with specific combos, so we need to know what your running.
FileMaker Pro Advanced 13.0v2 and Mac OS 10.9.2 and FileMaker Server 188.8.131.52. I tried what you recommended with the same problem. Here is the odd thing I found. If I make the layout longer than 1 page (I am using Portrait) the buttons do not appear in Preview.
If the layout is 1 page, the buttons do appear in Preview.
The layout has a Header which contains buttons only and a body which contains the fields and portals. Tried creating a new database. Same issue. As long as the layout is greater than 1 page, the button does not show up. If the layout is less than a full page, the button prints.
Post the new database that you created so it can be viewed to help trouble shoot this issue.
i can confirm the problem using OS 10.9 and FM 13. The problem doesn't occur with OS 10.6.8 and FileMaker 12. Looks like a potential bug. To work around this you could set up a situtation when you print to hides the button with the new Hide Object feature.
Just had a look at your test file. It's curious behaviour to be sure. For what it's worth:
1. Turning on sliding for the portal fixes it.
2. I tried creating a new layout with a portal containing a non-printing button with the same result.
3. I repeated 2. in a different file, this time configuring a field as a button, with the same result.
In each of my tests if the portal is set to slide the button does not appear in Preview mode; with sliding off it does. Ditto if the layout is set to exceed a page.
4. I opened each of the test files in FM12 and hiding behaviour was normal in all cases. Is this a FM13 bug perhaps?
I found using the Sliding up on the portal worked easiest, but it caused its own problems. I will list it as a bug. Thanks for the help.