Russia has many defects but things are. organised here. say, controlled :o)
If Putin authorized issue of a BUK to Donbass separatists, he'd surely accompany that by a whistle to own civil aviation. not by a whistle. by an order :o) - to avoid the conflict zone in planning their routes.
Any excuse would be used, easily, to cover up the real reason.
And, by the way, other world airlines would then follow Russian suit. Since many governments are used, by now, to read what Kremlin means - between the lines.
Nothing like that took place. To me that means the BUK system joining the fighting - if it were - was very un-planned for