The 81.1 version broke many saves using CLNE (LIGH) as heaters, as they are now generated properly (not just one pixel). Maybe a some kind of TMP or TMP2 value for the old spawning style?
Simon said the old way was a bug, so I don't know if he would do that. I thought of a way to fix it though. If there is VOID or something similar around the CLNE, it will just disappear, creating one pixel like the old way. I already did it here, so hopefully an official developer merges that commit in.