The previous fix for ticket [d85fffd6ffe856092ed8da] in check-in

[0a514e62ad1ebe5c12da8dae] did not completely address the
probably in that it only worked for cases where the OP_SCopy that loaded
the register was the last instruction in the sequence for the expression, which
is not necessarily the case for expressions like CASE...END.  This revision
prevents the registered that will be recomputed from being cached in the first
place.

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