Side effect causes the execution of a code which was not indended to

In certain cases WHEN doesn't prevent execution of a code.

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m := DATASET(['Should not appear'],

{STRING msg});
mf := DATASET(['Should not appear either'], {STRING msg}

);
tf := DATASET(['Should appear'],

{STRING msg}

);

w := OUTPUT(m, NAMED('MessageCodes'), extend);
falsearm := WHEN(mf, w, SUCCESS);
truearm := tf;

OUTPUT(IF(nofold(true), truearm, falsearm));
It is expected that output in w should not happen, since falsearm is not evaluated.
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It looks like the following code in Roxie:
virtual void stop(bool aborting)
{
if (state != STATEstopped)

{ stopDependencies(savedExtractSize, savedExtract, aborting ? WhenSuccessId : WhenFailureId); // These ones don't get executed executeDependencies(savedExtractSize, savedExtract, aborting ? WhenFailureId : WhenSuccessId); // These ones do }

CRoxieServerActivity::stop(aborting);
}
Is causing the dependencies to be executed – the code on the false branch is stopped (and aborting is false).
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