Summary and Info:
When a package upgrade moves some file from one directory to another, where the directories are symlinks to the same place, then pacman thinks this upgrade has file conflicts. But actually there's no conflict -- the old file would disappear when uninstalling the earlier version.

This is problematic for e.g. packages moving their files from /lib to /usr/lib. Case in point, openct: https://aur.archlinux.org/packages.php?ID=10155

Steps to Reproduce:
==== PKGBUILD v1 ====
pkgname=foo
pkgver=1
pkgrel=1
arch=(any)
build() {
mkdir -p $pkgdir/lib
touch $pkgdir/lib/foo
}

==== PKGBUILD v2 ====
pkgname=foo
pkgver=2
pkgrel=1
arch=(any)
build() {
mkdir -p $pkgdir/usr/lib
touch $pkgdir/usr/lib/foo
}

==== example ====
1. Build and install foo v1
2. Build foo v2
3. Install breaks:
# pacman -U foo-2-1-any.pkg.tar.gz
Targets (1): foo-2-1
(1/1) checking for file conflicts [############################################################] 100%
error: failed to commit transaction (conflicting files)
foo: /usr/lib/foo exists in filesystem
Errors occurred, no packages were upgraded.

# pacman -Ql foo
foo /lib/
foo /lib/foo