WHAT a poignant moment it was the other night when the BBC was sadly banished from STAR TV screens. Viewers from Pokfulam to Clear Water Bay watched this historic occurrence through tear-filled eyes. And they heard the BBC newsreader who was given the task of reading the last news bulletin before Rupert Murdoch pulled the plug sign off with Churchillian defiance: ''We hope to be back on your screens before too long.'' It would seem that this promise is going to be fulfilled sooner than any of us would have thought. For watching MTV on Monday night we were somewhat surprised to see trailers for BBC programmes being aired at frequent intervals on the pop channel. Could it be that STAR owner Murdoch has had a change of heart? Or has the carrier pigeon bearing the Murdoch edict somehow lost its way between Central and MTV's Hunghom complex, leaving the feisty station wonderfully ignorant of recent developments?