add debian bug report link for broken codenames

preferences.d/prefer-stable.pref

@@ -1,3 +1,6 @@
+# bugs in codenames:
+# https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=714726
+
 # target-release priorities should be >= 990 (and < 1000) apart from backports
 
 # Debian stable
@@ -5,12 +8,12 @@ Package: *
 Pin: release o=Debian,a=stable*
 Pin-Priority: 990
 
-# stable proposed-updates misses the "stable-" prefix..
+# stable proposed-updates misses the "stable-" prefix: #714726
 Package: *
 Pin: release o=Debian,a=proposed-updates
 Pin-Priority: 990
 
-# not working right now: bug in Release file: uses codename instead of stable
+# not working right now: #714726
 Package: *
 Pin: release o=Debian Backports,a=stable-backports
 Pin-Priority: 980
@@ -20,7 +23,7 @@ Package: *
 Pin: release o=Debian,a=testing*
 Pin-Priority: 890
 
-# not working right now: bug in Release file: uses codename instead of testing
+# not working right now: #714726
 Package: *
 Pin: release o=Debian Backports,a=testing-backports
 Pin-Priority: 880
@@ -30,6 +33,7 @@ Package: *
 Pin: release o=Debian,n=sid*
 Pin-Priority: 300
 
+# workaround for backports: #714726
 Package: *
 Pin: release o=Debian Backports
 Pin-Priority: 400