How to boot into the same OS you last used?

When using Boot Camp, what can I do to make my MacBook boot into the OS I last used?

Here is what I mean: I do not want to set a default OS. If I am using OS X and I do a Restart, I want the MacBook to automatically boot into OS X. If I am using Windows 7 and I do a Restart, I want the MacBook to automatically boot into Windows 7.

The only time I want my computer to boot into a different OS than the last one I used is if I manually choose to switch the OS by holding down the "Option" key at start-up. But after I manually choose an OS at start-up, I want the MacBook to automatically boot into the same OS if I do a Restart.

The problem I have right now is this: I am able to select a default OS, and no matter if I use OS X or Windows 7, it boots into the default OS when I Restart. For example, if Windows 7 is set as the default, even if I am using OS X, if I Restart, it will boot into Windows 7. Or, if OS X is set as the default and I am using Windows 7, when I Restart it will boot into OS X. That is not what I want. This is what I want: When I do a Restart or press the power button after a Shut Down, I want the MacBook to automatically boot into the last OS I used.

How do I do this?

 

wrldwzrd89, previously, my Mac used to behave exactly like yours. This is what I mean:

I've installed Windows 7 twice on my MacBook. The first time I installed Windows 7, my Mac was behaving exactly like you say your Mac is behaving now. Everything was fine. For reasons totally unrelated to Windows or Boot Camp, I decided to reformat my hard drive to do a fresh install of OS X. After that was done, I installed Windows 7, and now it is behaving differently, i.e., not like the way your Mac is behaving.

I wonder why it is behaving differently?