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satellites which kept at constant elevation encircling your house. I deem that 
rather unlikely. ;-)

As already mentioned (although theoretically possible), typically the 
positions of the satellites in the sky for such plots are not calculated from 
the GNSS data itself, but just from the orbit data (ephemerides) that either 
originates from the almanac sent by the GNSS constellation or is downloaded 
from the internet in your program together with your position and local time.

As you seem to have multiple traces entering the 'forbidden' region up to the 
north where no GPS satellites ever go with nearly constant elevation, it looks 
rather like a software bug of the plotting program to me. 

Or did you somehow do a gliding average of elevation and azimuth values 
separately and somehow the average was pulled there when az was zero
(see also Dana's post: "I own at least two Garmin handhelds that park out-of-
service sat symbols at due north on the horizon.")?

Cheers,
	Jürgen