Are exe/dll file copies linked to original location?

Using Win2003 sp1 and Win2003 sp2 (both ent editions), if I file copy an exe
or dll (location A) during software development to location B, if I rebuild
the exe/dll in location A, the copy that I put in location B seems to be
automatically updated?! Nice feature but what is it and how do I turn it off.
It's like a 'linked file'...and I wonder if it's related to my periodic
'Assembly not found' errors. They just come and go for no apparant reason...