Focus TDCi woes.

I had my Focus TDCi in for a service today. When I collected it, it was running roughly and billowing white smoke out the exhaust. This cleared
after they revved it for a while and appears to be normal now, with a clear exhaust. The rough running was due to air in the fuel system resulting from the fuel filter change, but I am a little concerned about the white smoke!
Does anyone reckon I have any cause for concern, or is smoke normal with air in the system?
Thanks for any advice.
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