The discussion of this bug started on the mailing list:
http://lists.alpinelinux.org/alpine-devel/1228.html

[I’ll post the resulting bug ID of this report back to that thread on the mailing list.]

Here’s what I’ve found out from the tests that I’ve run:

When doing:

sudo apk add ./package.apk

- For existing packages in system apk repositories:

• Same version + same pkgrel = apk downloads package from repository (X)
• Same version + newer pkgrel = apk installs locally-specified package (OK)
• For packages not in the system apk repositories:
  apk installs locally-specified package (OK)

‘Workaround’ for aports users:
->Increase pkgrel for existing aports.

Honestly, this could be a feature. I mean, is there truly a need to be able to install a local package of the same version and package release that’s available in one of the system apk repositories? At any rate, I will say that it’s definitely unexpected behavior, especially when you consider that you’ve specified a path to a local file.

(from redmine: issue id 492, created on 2010-12-10, closed on 2011-03-24)

• Changesets:
  • Revision 1c7e8d26 by Timo Teräs on 2011-01-01T14:58:58Z:

pkg: dependencies to specific package checksum

When package is installed from commandline, we should always
install that specific instance of package (never favor repository
version if it has difference identity). Otherwise we might not
always end-up installing the .apk given on command line. The
dependency is now against specific checksum identity (marked
with >< dependency comparison). Fixes #492.