In this video at about 7:15 in, the C210 is VFR at 8,500 inbound to DEN, and the pilot asks if they are cleared in the Class B airspace. The controller first clears them in, then about 10-15 seconds later climbs them to 9,000 and clears them to DEN via radar vectors and they are now IFR. No IFR flight plan on file, no request made, field was VFR, and they had VFR Flight Following until then.
Oops.
Oops.