How to stop Vim from opening a new window when opening file in readonly window?

Question

I'm using the MiniBufExplorer plugin to display a list of open buffers at the top of my Vim window. I'm also using the FuzzyFinder plugin to open files, in case that matters.

The problem is that, if I have the -MiniBufExplorer- window focused, and I open a file, the window will split:

MMMMMM     MMMMMM
AAAAAA     AAAAAA    M = -MiniBufExplorer-
AAAAAA --> AAAAAA    A = some open file
AAAAAA     BBBBBB    B = the file I just opened
AAAAAA     BBBBBB

My guess is that Vim determines that the -MiniBufExplorer- window should not be used to open a file in, and decides to create a new window to hold the new buffer.

Instead, I want file B simply to be opened in the window previously occupied by A. If A's window has focus, this happens the way I want it to; it's just when -MiniBufExplorer- is focused that I get the unwanted split.

I'm not proficient at Vim scripting, and not very familiar with the windowing/buffers model, so I don't know how difficult it is to accomplish this. Any ideas?