This bug is REALLY old... when the game is tied at '90 it runs normally and rarely shows the "end of 90 minutes" message, when you reload the page you will see that message inmediately after '90 (it looks exactly like no added time played).
As i said before, this bug is pretty old, sadly, it never were fixed
EDIT:
I just experienced this bug: As you can see, when the extra time is suposed to be playing, the "end of 90 minutes" message were displayed at '91:
http://imgur.com/N033Jyk,9vFquFIAfter reloading the page, that game situation in '91 happened in the extra time, not in "added minutes":
http://imgur.com/N033Jyk,9vFquFI#1It's a pretty old bug, nobody from the dev staff never seemed to care about it