I'm not really too sure how you can't repeat it... it does take a few windows to cause it though.

The bug isn't context-based so the Vista version is irrelevent. It's logic based. What you are asking it to do it put the window to the "back" of the stack of windows, then animate it away. This only works with maximised windows from what I could see, due to the nature of minimizing. 

There are likely to be a few reasons for this, as doing the normal thing and minimizing windows, and performing the relavent actions being carried out before the theoretically unnecessary action (animation) is carried out saves far more bugs than the little bug it creates. E.g. I use Windows+Tab a lot as well as Alt+Tab (depending on the context, and my mood). For the latter mostly, I don't even look at what I am doing, as I have the locations of the Windows in my mind. Rapidly minimizing the application followed by alt+tab and getting the same window back is far more confusing than no animation when you minimize.

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Wake me up in 2010 for W7. For now I'm waiting for Vista to boot.