So now I am really confused! Should pinning still be used with any Debian based distro, such as LMDE or SolydXK? Or should /etc/apt/preferences and /etc/apt/preferences.d/ have now gone from all systems?
if the user is using stock solydxk (i.e: no external repo. stay on UP system) then the answer is _pinning is not needed_. it was part from an era when wheezy was the testing. at that time LMDE decided to not using gnome stuffs from debian (because they were too old) and build their own MATE and Cinnamon. LMDE's package didn't compatible with debian's mixing them will ended up with disaster. thus, the pinning was created to make sure the system use the gnome stuffs created by LMDE team.
well...that was a story from wheezy era. when jessie comes the story goes different for solydxk and LMDE. LMDE decided to keep being not compatible with debian. they still build their own gnome stuff. the incompatibilities between LMDE stuff and debian stuff is still there and they need that pinning to make sure that the system is working. as for solydxk, we didn't build our own DE. all KDE and xfce stuffs are taken from debian, which means, we are 100% compatible with debian and the apt-pinning isn't needed anymore. in solyd, the packages is separated into different repo. both solyd and debian stuffs got their own repo and the content is completely different. thus, even if that pinning exist it doesn't mean anything and we could ignore it :3
hence, you can understand why did in my previous post I said using it on solydxk is useless. however, not every solydxk user is using the UP system. that pinning is harmless on stock solydxk but it posses some risk when user decided to jump into testing/sid or add other external repo. ZZ and some user adviced to remove it in order to minimalize the risk and make user easier to move into testing/sid. the team agreed and removed it (with the team policy to keep solyd and debian stuff separated, the risk is actually close to zero. however, ZZ and solyd team love solyd user so much and they were concerned about "the risk" so they stil remove it :3 ). the decision was made in early 2014. you still have that pinning because you were using an iso from 2013 era to install your system.
If pinning is no longer used then how are repo preferences determined?
by default all repo (except experimental) have 500 priority value. you can run 'apt-cache policy' command to check all repo priority.
there has been a scripting failure somewhere.
there's no scripting failure. in fact, there's no script ever created. the team removed that pinning from the latest iso but if user never reinstall his system then that file will not removed.
1. if user doesn't modify it, it's harmless.
2. there's a possibility that user have modified that preferences file. if we modify/or remove that pinning on UP, that UP will broke his system.
thus, the team decided to not touch that pinning and let the user remove it manually if he want to do it.