The Transform paradox
In Generation I if Ditto (or another Pokémon with only Transform) faces another Pokémon with Transform in a Trainer battle where neither Trainer has any items and no Pokémon besides the Pokémon with Transform, the battle will never end. This is because when Transform is used, the Pokémon will turn into its opponent, resulting in a Transform moveset of, again, only Transform. Since every time Transform is used, it gives the Pokémon using it the target's moveset with 5 PP each, Transform will continue to Transform into itself, restoring the PP every time it is used. Due to this, one will never reach a point where it can only use Struggle, unlike Wynaut and Wobbuffet in later generations who, although they too have no directly damaging moves, will eventually run out of PP and thus be able to use Struggle. This is likely why few Trainers have Ditto in the Generation I games.
This bug is not present in any other games because of a change in Transform mechanics: from Generation II onwards, it is not possible to Transform into a Pokémon that is the Transformation of another Pokémon.
This is from Bulbapedia's page for the move transform this probably remains true for Imposter as it "Transforms" upon being sent out. So the second Ditto's ability would fail and it would remain a Ditto.