Hi Nathan,
If this is a batch campaign then it should include the leads that meet the smart list criteria at the time that it runs.
If this is a triggered campaign with a wait step, then I could see a scenario where the lead could enter the campaign, change status, and then still be a member for subsequent flow steps.
Once a lead has entered a campaign flow, later changes that may make them inelgibile for the campaign based on the smart list critieria will not automatically remove them.
Another thing to look at: what type of field is "SFDC Type" in your instance? If it is a formula field, these do not by themselves trigger the Marketo-SFDC synch and so the formula could have updated in Salesforce but Marketo included the lead in the campaign based on older data.