Julie Zeien (12/16/2009)
I apologize for the incorrect explanation. I ran into a problem with this sort of thing about 3 months ago, and I looked all over BOL EXCEPT for the decimal data type page. Oops. I thought this was an undocumented problem, so I played with it for a couple hours and came to an incorrect conclusion. Hopefully Steve can fix it. Thank you to those who knew the correct reason behind this.
Unfortunately it's very easy play with something for a while, form a mental model of what's going on, then try a few tests to check the model and when they work believe it is true. So don't worry to much at having done it - we all do it sometimes. The great trick is to find some tests that will check all the edge conditions implied by the model, which is sometimes very hard to do.
Tom