Search parameters are all evaluated independently. The location parameter and the location-period parameter are thus going to be executed independently. You'll get matches for encounters that were at that location at some point, and encounters that were in some location at that period, but you won't get encounters that were at that one location at that one time. (It also breaks if you list multiple locations or multiple periods, which is also legal.)

location-period should be changed to be a composite where you pass both a reference and a period.