Mark, 
I'm not sure if this is even documented, 
I find this a bit inconsistent when compared to the behavior of other statements, 
E.g.: 
* list expressions do have their scope and do not overwrite local variables
* with statement does overwrite the variable value but makes it available even after with block 
* except overwrites variable value, but then the value gets cleaned and no longer accessible. 

I do understand why this happens, but I find this undesirable. At least some consistency will be nice to have, or this should be documented. Otherwise, it confuses.