In case a jobs workspace does not exist, these actions don't work:

• SCM changes are not shown
• SCM polling says "workspace doesn't exist, running the job now to populate the workspace"

When creating an empty folder where the workspace should be SCM polling and SCM changes work normally again.

At least for accurev this does not make any sense to my knowledge.
There is no information stored in the workspace and so I cannot see a reason why it should not be able to show the SCM changes in case the workspace does not exist on disk. Same is true for SCM polling: The information is not stored in the workspace so there is no need to have the workspace in order to figure out from the SCM if something is changed.