Hi,
It is indeed a bug. We plan to fix this in an update for ARCHICAD 22 later this year. You will find it in the Release Note as fix #259466.
It was never possible to stretch stairs with the marquee, but you could drag them. As a workaround you can still drag the stair with the marquee, if you draw the marquee box, and press ctrl+D.
Regards,
Daniel Alexander Kovacs
Professional Services Consultant
GRAPHISOFT
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