I was unable to recreate the problem given the test case provided and the following version of grep:
$ apt-cache policy grep grep: Installed: 2.23-1 Candidate: 2.23-1 Version table: *** 2.23-1 500 500 http://mirrors.cat.pdx.edu/ubuntu xenial/main amd64 Packages 100 /var/lib/dpkg/status
I was unable to recreate the problem given the test case provided and the following version of grep:
$ apt-cache policy grep mirrors. cat.pdx. edu/ubuntu xenial/main amd64 Packages dpkg/status
grep:
Installed: 2.23-1
Candidate: 2.23-1
Version table:
*** 2.23-1 500
500 http://
100 /var/lib/