I'm confused

Just taking a look at the Newmarket Holidays website which is offering flights from Manston to Dubrovnik next year, it says the flight is being operated by Tor Air yet the airline code is OA, Olympic Air and a bit more delving seems to reveal that it's actually a Small Planet a/c that's operating the flight.
I wouldn't mind booking it (mainly because I enjoy using Manston) but having also read some of the above postings I am now a little wary to say the least, is this all fairly standard practice?