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When a sortkey contains a pipe, the API can return a continuation like:

<query-continue>
 <categorymembers cmcontinue="Bar|Baz|" />
</query-continue>

When using that, the API obviously returns the error message:

<error code="cmbadcontinue" info="Invalid continue param. You should pass the original value returned by the previous query">

The same issue may apply to other modules that use non-title-validated strings in continue parameters (if there are any other ones).