This refers to the (closed) bug #141908. If possible, could you re-enable that feature in urxvt, maybe making it useflag controlled. "Fixing" that bug by removing this function was not really necessary, as first comment in that bug suggest. Reproducible: Always Steps to Reproduce:
Well, we don't control breakage by use flags, sorry. If you have a real fix, feel free to reopen. :)
#define SCROLL_ON_UPDOWN_KEYS needs to be uncommented out in feature.h, or added as a CFLAG. I've verified that this works.