I'm not yet convinced that there are any bugs in the archived copies of the game (at StairwayToHell and bbcmicro.co.uk) that weren't also in the original release.
The bugs that iamaran and I have identified, above, might have been present in the copies of the game that were played by the writers* of the reviews that have been posted in the thread so far. There's nothing to say that the bugs
weren't present in those review copies.
And I've found some evidence that the tapes that were sent to magazine reviewers
were problematic. In the April 1988
issue of Micro User, the Mad Hatter mentions that the game on the B-side of the Alien From Outer Space tape displayed some unusual behaviour: "the text descriptions went all peculiar every time the graphics appeared"!
More pertinently, he also complains about the quirkiness of the syntax required by Alien From Outer Space: he found that if an OBJECT was in a CONTAINER, he couldn't just say GET OBJECT -- he had to explicitly say GET OBJECT FROM CONTAINER, which chimes with the behaviour we're seeing in our archived copies of the game today.
So maybe the original release of Alien From Outer Space was itself a bit buggy..?
* All of whom were, I suspect, Barbara Gibb!