Per-session (-1) cookie lifetime not working

When cookie expire (days) is set to -1 plugin pops up every time. This is because -1 is treaded as day and multiplied by 24*60*60*1000. I can fix it by changing:
expires=”+date.toUTCString()
to:
expires=”+(ms<0 ? “-1” : date.toUTCString())
Then it works as expected – please provide a fix.