To my knowledge long time ago

select xyz && current
replace xyz1.f1 with xyz2.f2 in xyz1 
* or 
replace f1 with xyz2.f2 in xyz1 

but "in xyz1" was required in both cases to make it happen in xyz1.
It turned out at least in VFP9

replace xyz1.f1 with xyz2.f2  && implicit  in xyz1

does work. If I am not mistaken in thinking that "in non_current_alias" was required long time ago, just wondering, when did this change happen ?