In the Razor mediator, imports are essentially a text replace before the containing template gets compiled. To get a new version of the include to be used, you need to ensure that the mediator "realises" that the including template needs to be recompiled because the current cached version is out of date. There are two main approaches to this:
- Update the containing template with some trivial change (easiest is to update the Title, Save, Change the title back, Save and close)
- Restart the process that hosts the Mediator and its cache. When publishing, this will be the publisher. When previewing, it will be the service host. (Knowing that preview's cache is distinct from the publisher's cache will save you much grief.)
Edit: You should also be aware that the mediator can be configured to impersonate another user when loading dependencies. In this scenario, only the checked-in version will be available, as the workflow version belongs to another user. I think it's possible to use the mediator without doing this, but there will be functional trade-offs. Check the mediator documentation for the relevant settings.