Specific case: Any style using the lemming sprites from gigalem_millas seems to reproduce this issue in low-res mode only. Can confirm that xmas, and default with or without recoloring, do not reproduce it, in either resolution.
Instead of displaying as it should, it only shows a single lemming facing right. It can still be distinguished from the Walker pickup by the positioning of the lemming, though this is a very subtle difference. (See attachment - left = walker; right = cloner.)
Fixed in e2c434f, backported to 12.8 in 4a69501.