Paul Corfield wrote:
Well yes but OSIs have "sides" that are logically paired. If you
re-enter the same side that you exited from it should not continue the
original journey. More detail on precisely what the OP did would
confirm whether the OSI acted properly or not.

Exitted old Northern line (etc) gateline; back through the
new one just to see what it was like (eg any more accessible
with luggage etc). Local station was Canada Water.

#Paul