I have a bug report, sometimes compressed deut gives in reaction with neut cold neut sub-zero. I know this is probably mentioned before, this happens rarely and oftens stops when restarting, but besides that I hope it get's fixed or there is an explanation which states why this can happen.
edit: It doesn't goes away now (I will try to make a save which shows it)
edit again: doesn't works to make a save that shows it but make a ball of coal or any other material make it hollow and fill it with deut (floodfill) then with console you make the life higher !set life deut 87238772 or something like that and then place neut in the middle and in heat display *6* then you will see subzero neut.