This posting on bbc states it was military testing satellites on gps tests of some kind. While fishing Sat. My TI 7 would hardly draw a broken track and most times my mapping was totally off on my waypoints. I was ready to throw it in the lake. It never affected my Helix Mega 9 for some reason.
Time not showing up on HDS units? - Page 3
if you read the thread, there is a schedule of military testing that is/was happening in diff. Parts of th US.