It sounds like something might have been incorrect with the flow in your campaign, but a simple data maintenance program should be able to fix it.
Set up a smart campaign with the smart list:
Lead was Synced to SFDC = (date you synced the leads)
Lead Source = "web lead"
Then the flow:
Change data value - Attribute: "Lead Source" New Value: "event"
If the program you initially made changed the lead source, then that means your fields are mapped correctly. If you think it was SFDC that changed it (you could look in the lead history, assuming you are tracking changes for that field), then you might want to check your workflows, field updates, or default values. Something weird could've happened in that area as well.
Hope this helps!
Keith,
Thank you for the above steps, that was extremely helpful!! The default values looked fine (nothing was checked as default), but when i navigated to the field updates, I found this:
I am not sure what this is or what its purpose is. I'm assuming if I just delete this, it may resolve the issue?