I was trying to tell you what the reason is for the patch. I will start by saying I don't know the exact changes that were made in 943460. But I will say I'm sure a lot depends on the application at hand, the file at hand, etc. The problem that was addressed by this was widely known (all the PDF spam as of late).
Anyway, for where the issue is coming from, an application, or Windows itself can take a command-line of a document and associate it to a specific application and then open it. This is what Windows does upon a double-click in Explorer (which is the desktop as well).
Now the process then becomes an act of sending a URI to a program, and the program receiving a URI. Basically, though, it's a call to "ShellExecute" in the DLL that is patched in this security update. To look at your other thread, Explorer calls "ShellExecute", which in turn runs the application configured in the shell for "XLS".
Again, I don't know what the code is doing on this new patch (to know that fully I would have to know how to do the exploit in question, and I don't), but it seems the patch might be picking certain known attack vectors (XLS would be one of those, but CSV is not, since it's plain text), and interpreting the passed URI more strictly. Hence, either it is passing three URIs now, or Excel is interpreting the URI as three files.
To use another example illustrating what is going on, I have a COBOL compiler here that was written in the 9X days. The problem with it for XP (or even 98/ME) is that I can't put a source file into a LFN directory and open it via double-click because the compiler interprets the sent URI in much the same way as your excel example. I try to open a source file in "C:\My Documents\Source Files", and it complains about not being able to open "C:\My".
To that end, a lot of how URIs are handled is dictated by how the extensions are configured in the system. For the systems in question, you might try going into Explorer under the File Types section, and look at XLS then go to the Advanced section and look at the definition for "Open" and see if it can be changed. For example, my XLS definition for "Open" is:
Code:
"C:\Program Files\OpenOffice.org 2.3\program\soffice.exe" -calc -o "%1"
Notice the quotes around both the executable path and %1 (the parm used to pass the URI to the program). It may be that the configured call for XLS might not have the " around %1.
Hope that helps, or at least clears up the confusion some.