ag ignores files in a directory called 'lib'

gistfile1.txt

tdhopper@~/temp $ echo "hello" > file1.txt
tdhopper@~/temp $ mkdir lib
tdhopper@~/temp $ cp file1.txt lib/file2.txt
tdhopper@~/temp $ mkdir dir2
tdhopper@~/temp $ cp file1.txt dir2/file3.txt
tdhopper@~/temp $ ag hello
dir2/file3.txt
1:hello

file1.txt
1:hello
tdhopper@~/temp $ ack hello
dir2/file3.txt
1:hello

file1.txt
1:hello

lib/file2.txt
1:hello