Since when are the Bruins a nerve-wracking team to watch? Since when does a third-period lead mean a good chance of a nail-biter and a pretty good chance that they won’t come out of it with any points? 

In allowing the Jets to come from behind in the final 10 minutes of the third and hand the B's a 3-1 defeat Tuesday night in Winnipeg, the Bruins suffered their latest regulation loss in a game in which they held a third-period lead.

Here’s a maddening delivery from the WEEI.com stat truck: 

- The Bruins have lost six games in regulation (19-6-3), and they’ve led in the third period of five of them. Yaysh. 

- The B’s have entered the third period leading 14 times this season and are 9-4-1 in those games. That gives them a .643 win percentage, which is 29th in the league. Double-yaysh. 

- Of the bottom 10 teams in the NHL when leading after two periods, the Bruins -- second-worst in the league in this category -- are just one of two teams currently in line for a playoff spot. Yaysh to the max. 

You can watch this happen time and time again and think that it’s unlike the Bruins to let leads slip away like this, but after they’ve done it enough times -- say, six (including their overtime loss to the Capitals) -- it is very much like them. It’s something that they do and something that they continue to do. 

So, to borrow Bill Belichick’s “When you sign a player you get everything that comes with them” logic, when you assess the 2013 Bruins, you have to include this tendency as a big part of it. They have strong goaltending, a great defense and two very good lines. They stink on the power play, they’re usually nutbars on the penalty kill, and they blow third-period leads. And when they blow them, they usually don’t even get a point (0-5-1 in games in which they’ve seen third-period leads erased). 

Yes, it’s a departure from the early days of the season, when the B’s would either take the lead or add to it in the third period. The B’s outscored their opponents 7-0 in the third period over their first six games of the season and had a perfect 6-0-0 record to show for it. Then, after taking a 4-3 lead 1:45 into the third period of their seventh game of the season against the Sabres, they allowed four unanswered goals and lost.

Since that loss -- their first of the season -- many of their regulation losses have looked similar. In fact, Sunday’s loss to the Penguins was the first time this season that they lost the old-fashioned way: by a team grabbing a lead against them early (like Pittsburgh’s 2-1 lead after the first period) and holding on to it. All of the B's other regulation losses were on track to be wins until the final 20 minutes of the game. 

You would think that by now, this wouldn’t be a case of the Bruins simply getting the lead and then trying to cruise. They know better than anyone how unfortunate some of these third periods have been, so at this point they should be getting up to defend third-period leads as if they were trying to prevent a loss. As dumb as that logic sounds, they actually have lost half of the last eight games they’ve gone into the third period leading (4-3-1), so if they were to respect recent history they would actually enter such third periods feeling they had something to prove. 

Earlier in the season, the Bruins’ well-executed approach was simple: Get points out every game, because the value of a point is much greater in a 48-game season. They did that better than any other team in the East to begin the season. If they fell behind, they would be the ones to come back in the third period, as they did when they erased a three-goal deficit against the Rangers on Feb. 12. Their 2-1-2 record and .400 win percentage when trailing entering the third period puts them third in the league in such scenarios. 

Now, they’re squandering points in the worst way. They don’t let teams come back and take them to overtime; when they blow it, they blow it in grand fashion and get nothing out of it. The Bruins have been one of the best teams in the NHL this season, but there’s no denying their third-period Achilles’ heel.

It was earlier in the season when the Bruins seemed to understand better than any Eastern Conference team that it’s a 48-game season. With 20 games left in the regular season, they need to be reminded that it’s a 60-minute game.