AdiIRC

Ok i tried to reproduce it in a clean AdiIRC 64bits under Windows 11 and i did.

Steps to reproduce :

1. Paste any code there like for example the one i provide here.
2. Resize the editor, make it smaller, try to play with the dimensions. (like the attached image for example)
3. Try to scroll down the mouse wheel at the bottom and then it will trigger.

Code :

big { ; by Racoon (adiirc fix by Ouims)
  if (!$0) { return }

  var %big = $chr(32) $+ !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`{|}~
  var %big1 = .. .xx. xx..xx .xx..xx. xxxxxxx. xx..xx .xxx.. .xx ...xx xx... ...xx... ...... ... ...... .. ....xx .xxxx. .xxxx xxxxx. xxxxx. ...xxx. xxxxx .xxxx. xxxxxx .xxxx. .xxxx. .. ... ....xx ...... xx.... xxxxx .xxxx. .xxxx. xxxxx. .xxxx. xxxx.. xxxxx xxxxx .xxxx. xx...xx xxxx ....xx xx..xx xx... xx....xx xx..xx .xxxx. xxxxx. .xxxx.. xxxxx. .xxxx. xxxxxx xx..xx xx....xx xx...xx xx...xx xx..xx xxxxxx xxxxx xx.... xxxxx ..xx.. ...... xxx. ...xx .xx. xx... .xxx.xx
  var %big2 = .. xxxx xx..xx xxxxxxxx xx.xx... ...xx. xx.xx. xx. .xx.. ..xx. xxxxxxxx ..xx.. ... ...... .. ...xx. xx..xx xx.xx ....xx ....xx .xx.xx. xx... xx.... ...xx. xx..xx xx..xx xx .xx ..xx.. xxxxxx ..xx.. ...xx xx..xx xx..xx xx..xx xx..xx xx.xx. xx... xx... xx.... xx...xx .xx. ....xx xx.xx. xx... xxx..xxx xxx.xx xx..xx xx..xx xx..xx. xx..xx xx.... ..xx.. xx..xx xx....xx xx...xx .xx.xx. xx..xx ...xx. xx... .xx... ...xx xx..xx ...... ..xx ..xx. .xx. .xx.. xx.xxx.
  var %big3 = .. .xx. ...... .xx..xx. xxxxxxxx ..xx.. .xxx.x ... xx... ...xx .xx..xx. xxxxxx xxx xxxxxx .. ..xx.. xx.xxx ...xx ..xx.. .xxxx. xx..xx. xxxx. xxxxx. ..xx.. .xxxx. .xxxxx .. ... xx.... ...... ....xx ..xx. xx.xxx xxxxxx xxxxx. xx.... xx..xx xxxx. xxxx. xx.xxx xxxxxxx .xx. ....xx xxxx.. xx... xxxxxxxx xxxxxx xx..xx xxxxx. xx..xx. xxxxx. .xxxx. ..xx.. xx..xx .xx..xx. xx.x.xx ..xxx.. .xxxx. ..xx.. xx... ..xx.. ...xx ...... ...... .... xx... .xx. ...xx .......
  var %big4 = .. .... ...... xxxxxxxx ...xx.xx .xx... xx..x. ... .xx.. ..xx. xxxxxxxx ..xx.. .xx ...... .. .xx... xxx.xx ...xx xx.... ....xx xxxxxxx ...xx xx..xx .xx... xx..xx ....xx xx .xx ..xx.. xxxxxx ..xx.. ..... xx.... xx..xx xx..xx xx..xx xx..xx xx... xx... xx..xx xx...xx .xx. xx..xx xx.xx. xx... xx.xx.xx xx.xxx xx..xx xx.... xx..xx. xx..xx ....xx ..xx.. xx..xx ..xxxx.. xxxxxxx .xx.xx. ..xx.. .xx... xx... ...xx. ...xx ...... ...... .... ..xx. .xx. .xx.. .......
  var %big5 = .. .xx. ...... .xx..xx. .xxxxxxx xx..xx .xxx.x ... ...xx xx... ...xx... ...... xx. ...... xx xx.... .xxxx. ...xx xxxxxx xxxxx. ....xx. xxxx. .xxxx. xx.... .xxxx. .xxxx. .. xx. ....xx ...... xx.... ..xx. .xxxxx xx..xx xxxxx. .xxxx. xxxxx. xxxxx xx... .xxxxx xx...xx xxxx .xxxx. xx..xx xxxxx xx....xx xx..xx .xxxx. xx.... .xxxxxx xx..xx xxxxx. ..xx.. .xxxx. ...xx... .xx.xx. xx...xx ..xx.. xxxxxx xxxxx ....xx xxxxx ...... xxxxxx .... ...xx .xx. xx... .......

  set -eu0 %_bigrb $iif(%_bigrb,$gettok($v1,2-,32) $gettok($v1,1,32),$regsubex(4 7 8 9 11 12 2 6 13,/(\d+)/g,0 $+ $chr(44) $+ \1))

  var %string = $regsubex($replace($upper($1-),$chr(160),$chr(32)),/[^\Q $+ %big $+ \E]/g,)

  var %i = 1
  while (%big [ $+ [ %i ] ] $+ ) {

    var %bigi = $v1
    var %bigi $regsubex(rac,%string,/(*UTF8)(.)/g,$nestednoob(\n,%bigi,%big,%_bigrb,\1))

    $iif($show,say,echo -a) $$replace(%bigi,x,.,.,$chr(160))

    inc %i
  } 

  if (!$event) && (!$editbox($active)) editbox -ap $iif($show,/big,/.big)
}
nestednoob { var %_bigrb $4,%n $1 | returnex $regsubex(coon,$gettok($2,$poscs($3,$5),32) $+ $chr(32),/(x+)/g,$chr(3) $+ $gettok(%_bigrb,$calc(( %n -1) % 9 +1),32) $+ \1 $+ $chr(3)) }