It's possible that this is another manifestation of a bug recently reported here:
For More Information see: Huge oversight on FM12 tab panel implementation
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
Thank you for your post.
I am able to replicate the issue on both Mac OS X 10.7.3 and Windows XP. A similar issue was reported in reference to Tooltips being accessed behind a transparent object:
I have forwarded your post along with my findings to our Development and Testing departments for review. I will keep you updated as information becomes available to me.
The solution to this problem (FileMaker 12 portal won't scroll with trackpad or mouse wheel) is to bring the portal to the front in layout mode.
You can do this by selecting the portal, then choose Arrange -> Bring To Front.
FileMaker 12 has very weird issues with the "layering" of objects... these problems were not in earlier versions of FileMaker, but now they are prevalent in FileMaker 12. If FileMaker doesn't think that the portal is the very frontmost object of the entire layout, then you won't be able to scroll through the portal with your trackpad or your mouse wheel.
When this problem crops up in FileMaker 12, what this means is that some object with a transparent middle (such as a box that has a visible edge but a nonvisible middle) is actually LAYERED ON TOP OF YOUR PORTAL, even though you probably think that your object is BEHIND YOUR PORTAL.
In our circumstance, we always draw boxes with transparent middles as the BACKGROUND of our layouts... but in FileMaker 12, it believes that those boxes are at the VERY TOP of our layouts. So the solution is to either send the boxes to the back, or send the portal to the foreground.