Wood burning stove letting smoke into house

We have a wood-burning stove in out four seasons porch. Last winter it worked perfectly. We started using it again last week, and after about 10 minutes of a fire being lit, smoke billows out of the vent on the right side of the stove (not the vent that you turn to open and close. The vents that are on the top, left and right sides of the stove). We had the chimney cleaned yesterday. He said he didn't find anything blocking the chimney. But today, when we let another fire, after 10 minutes, smoke again came out of the right vent.
Any ideas?
Thank you.

The guy didn't close the damper, did he?

What happens if you just light newspaper? Any possibility of a temperature inversion? That's the only time we get a down draft.