Hi Dom,
Enable DWF Attachments in server settings does not ensure DWF files will be created by task schedule.
The designed workflow to add file with DWF in task schedule is:
1. Add the project to task schedule
2. If you'd like the file be added to Vault immediately, check "Immediately"
3. Click OK on task dialog, a "Check In Files" dialog will prompts
4. Click Settings button on the dialog, check "Create DWF Attachments"
The setting in step4 will decide whether DWF file will be published while adding files by task schedule.
Hope this helps!
Regards,
Carol