had a similar incident on a flight out of Exeter to Dublin weekend before last, main gear doors started doing their own thing about 15 minutes out, and with other aspects of the way we returned to Exeter, the prime suspect was hydraulic fault of some sort, but getting a reply on what's going on has proved to be very hard.
It's clear that the Dash 8 has some issues at the moment, I've seen too many threads in here recently about returns, or shut downs or diversions, and I don't think it's a maintenance issue, but exactly what is happening is shrouded in mystery at the moment.