A little more information in your first post would have gotten us here sooner.
I'm still not sure what behavior you are seeing. I am confident that we can sort this out. Unfortunately for us, Apple has done an exceptionally poor job naming the various interface elements that we use to display the data in our database.
As you know, there are some top-level Views, and (confusingly), different Views for each of these top-level Views. Let's us call the class of top-level Views "Viewing Modes", and stick with Apple's term for the subordinate "Views".
The top-level Viewing Modes include the three that are regularly used: Browser Mode, Viewer Mode (exceptionally-badly named), and Split View Mode (which is, simply, a two-pane mode showing one Browser and one Viewer).
Other top-level Viewing Modes not relevant to this discussion are Projects View (mode), Places (mode) and Faces (mode).
The Browser has three subordinate Views that allow you to display the information available in different ways: Grid View, List View, and Film Strip View. (Film Strip View is available only when in Split View.)
You can cycle between the three regular Views by typing "v". (This even works when in a Book Album, which is clever.)
In sum, so far, these are the Viewing Modes and Views in Aperture:
- Projects (confusingly named)
- Places
- Faces
- Photos (or a Project or Album or multiples thereof)
- Browser
- Viewer
- Split View (one Browser and one Viewer)
- Film Strip View (for Browser), in addition to Grid View and List View
Double-clicking an Image in a Browser changes the Viewing Mode to Viewer Mode (this is precise); double-clicking an Image in a Viewer returns the Viewing Mode to either Browser Mode or Split View Mode (whichever was last used).
(Just to be complete, note, too, that Aperture allows multiple top-level Views of the Browser to be shown either at tabbed panes or as tiled panes. This setup shares the Viewer when you switch to Viewer or Split View. It is useful and worth learning about.)
It gets more complicated .
What you see in the Viewer depends on how many Images are selected, which Viewer View you are using, and whether or not you are in "Primary Only" View.
Just like the Browser has three Views (Grid, List, Film Strip), the Viewer has five. They are:
- Viewer Mode
- One
- Multiple
- Three-up
- Compare
- Stack
(All of these are found on the "View" menu.)
Multiple View shows you all selected Images (up to eleven, after which you'll see a small notice indicated how many more are selected and not displayed). This is the most common Viewer Mode View, and should be used as the default. When only one Image is selected, it shows one Image.
One View shows just one Image. When more than one is selected, it will show the Primary Selection (this Image is indicated by a heavier selection border). Note that you can cycle through the selected Images without exiting Viewer Mode and without changing the selected Images by using the {semi-colon} and {apostrophe} keys. (The arrow keys will lose the selection as soon as you arrow to an Image not in the selection.)
In your case, you might find it useful to either advance/retreat through the selected Images while staying in Viewer Mode's One View, or to, also staying in Viewer Mode, toggle between One View and Multiple View.
Three-up View shows the current Primary Selection in the middle, flanked by the previous and next Images, either within the current selection, or, when only one Image is selected, outside the selection but in the current container's Browser. Three-up view is very useful for making the same adjustments to a series of Images: you can see the results of the adjustment alongside the current Image and the next one to be adjusted. (I use this all the time when cropping sets of Images, for example. I advance to the next Image and confirm the crop I just did without ever closing the Crop Adjustment.) Three-up View is available when multiple Images are selected, but does not, to me at least, provide any utility or make any sense.
Compare View and Stack View are devoted to a particular process. I have never found them useful (there are better processes to accomplish the task to which these Views are dedicated). Details on how to use them are here and following in the User Manual.
"Primary Only" is selected from either the "Edit" menu or the Viewer's Tool Strip. This makes sense, because it does not effect which Images you see on-screen. It forces any adjustments or metadata changes you make to be applied to only the Primary Selection. When Primary Only is selected, you will see, in Viewer Mode, only the Primary Selection has a Selection Border.
Before returning to your issue, I want to add a suggestion that everyone change the keyboard shortcuts associated with the Viewer Modes and Views. Here is what I use for Viewing Modes:

Note that C, V, B, N, & M are all in a row (on an English keyboard), F is nearby and makes sense, and all six can be keyed with one hand.
Here is what I use for Viewer Mode Views:

Seems sensible to me. Also all keyable with one hand (my left, so I don't have to put down my Wacom stylus).
And here is what I use for Browser Mode Views (all defaults, iirc):

Now returning to your issue. I'm not sure, from your description, what is happening. The above, while lengthy, should give you the information you need to trouble-shoot the problem. I don't know what you mean by "the single photo button ". If the above does not help you resolve your issue, it indicates that Aperture is not working properly. The common cure for interface malfunctions is to delete your User Preferences. Details are on Apple's Aperture trouble-shooting page.
Please post back with what you do and find out.
HTH,
--Kirby.