What branch source are you using in this example? (E.g., config.xml of multibranch project.) And what software versions? I would need to be able to reproduce from scratch, since there has long been automated test coverage demonstrating that the same revision is checked out each time. Also please attach the build log.

FWIW this is not a new regression, we noticed this ages ago, and have been using stash/unstash for ~6 months.
I hadn't realised this wasn't intended behaviour.

config.xml consoleText.txt

Nothing complicated, just a normal project, not a multibranch project, see attached.

Jenkins version 2.30, I updated all plugins yesterday, I can give you specific versions, but here are the pipeline ones:

```
Pipeline: API - 2.6
Pipeline: Basic Steps - 2.3
Pipeline: Build Step - 2.3
Pipeline: Declarative Agent API - 0.5
Pipeline: Groovy - 2.22
Pipeline: Input Step - 2.3
Pipeline: Job - 2.8
Pipeline: Milestone Step - 1.1
Pipeline: Model API - 0.5
Pipeline: Model Definition - 0.5
Pipeline: Multibranch - 2.9
Pipeline: REST API Plugin - 2.2
Pipeline: SCM Step - 2.2
Pipeline: Shared Groovy Libraries - 2.4
Pipeline: Stage Step - 2.2
Pipeline: Stage View Plugin - 2.2
Pipeline: Step API - 2.5
Pipeline: Supporting APIs - 2.10
```

just a normal project, not a multibranch project

As the documentation for scm in Global Variables Reference notes, currently the idempotency guarantee is made only for multibranch projects. (Because the traditional Jenkins SCM API is too weak to do this.)

Oh! Sorry, that's easy to miss! Thanks for the clarification.

Probably a variant of CpsScmFlowDefinition based on SCMSource could be constructed which would give the same guarantee as a multibranch project—basically it would act like a single branch project without a parent folder. Only certain SCMs would be compatible.