This is a migrant and winter visitor to Thailand. It was formerly considered a race of the Red-breasted Flycatcher (F. parva). This photo shows the jet black uppertail coverts which help distinguish it from F. parva.
The species was common in a variety of habitats, often seen on low perches and dropping to the ground. They frequently cocked their tails while giving harsh buzzy calls. I was particularly keen to see this species after missing a "one day wonder" that showed up in California in October 2006.
Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope III | 30XWA |hand-held (no adapter).