There seems to be a number of SNAPSHOT related issues, so I'm going to make an epic issue to track them, and perhaps discuss expected behavior around SNAPSHOT.

expectations/requirements

Re-resolution

R-1.1. Assuming the dependency graph stays constant, calling compile should NOT re-resolve SNAPSHOTs.
R-1.2. Starting up sbt should NOT re-resolve build or meta-build. This is partially due to IDEs spawning sbt from shell repeatedly.

Force

R-2.1. Calling update re-resolves SNAPSHOTs.
R-2.2. To short-circuit or check all resolvers. (configurable?)
R-2.3 The list of resolvers to look for SNAPSHOTs. (configurable?)
R-2.4 Subproject re-resolution should be cached.

Maven local m2

R-3. Should work with local m2.

existing issues

Resolver mixup

• SNAPSHOT dependency does not get resolved while compiling a dependent project after publishing depended-on jar to remote repository when both operations are on the same box. #1495 SNAPSHOT dependency does not get resolved up while compiling a dependent project after publishing depended-on jar to remote repository when both operations are on the same box

Short circuiting

• sbt doesn't see new SNAPSHOT dependency versions #1514 sbt doesn't see new SNAPSHOT dependency versions (Fixed but not enabled by default)

Classifier

• sbt SNAPSHOT dependency with classifiers not updating #641 sbt SNAPSHOT dependency with classifiers not updating
• SNAPSHOT dependency with classifiers not updated #1676 SNAPSHOT dependency with classifiers not updated
• updateClassifiers doesn't download sources and docs for updated snapshot dependencies #1750 updateClassifiers doesn't download sources and docs for updated snapshot dependencies

Maven local m2

• SBT doesn't see new SNAPSHOT dependency versions in local maven repos  #321 SBT doesn't see new SNAPSHOT dependency versions in local maven repos
• SNAPSHOT dependency not updated #1061 SNAPSHOT dependency not updated
• Maven local resolver with parent POM #1616 Maven local resolver with parent POM
• publishM2 doesnt write maven-metadata-local.xml which make SNAPSHOT work near impossible #2053 publishM2 doesnt write maven-metadata-local.xml which make SNAPSHOT work near impossible
• Fail to download the first SNAPSHOT publish to Artifactory #2088 Fail to download the first SNAPSHOT publish to Artifactory

Offline

• SNAPSHOT won't work offline #1552 SNAPSHOT won't work offline
• Cannot parse snapshot xml from local ivy while offline #1824 Cannot parse snapshot xml from local ivy while offline

Continuous

• Avoid updating snapshots in continuous run mode #1446 Avoid updating snapshots in continuous run mode

Maven SNAPSHOT/uniqueVersions support

• Incorrect Maven Snapshot file resolution #679 Incorrect Maven Snapshot file resolution
• SBT doesn't honor Maven's uniqueVersions #1322 SBT doesn't honor Maven's uniqueVersions
• SBT does not replace SNAPSHOT with a date when publishing #1564 SBT does not replace SNAPSHOT with a date when publishing