Looking in my SE Asian bird book (Field Guide to the Birds of Thailand and South East Asia by Craig Robson) I don't think that it is a chestnut-tailed starling (sturnus malabaricus) beause that would have a paler head than the underparts and this bird is the other way around. Unfortunately I don't have any better ideas
I'm still convinced that chestnut-tailed starling is the best fit I've come across. EDIT: found some striking photos of subspecies nemoricola: Oriental Bird Club Image Database : Chestnut-tailed Starling » Sturnus malabaricus Oriental Bird Club Image Database : Chestnut-tailed Starling » Sturnus malabaricus
I can see where you're coming from. Shame the tail is out of sight. That first image you posted is lovely.