Ulster's players broke into song when they won a friendly for the first time on French soil last August, but there was no singing coming from their dressing-room on Saturday when they were victorious there in a competitive fixture for the first time in 15 visits.
Ulster may have finally broken their French hoodoo, but this was a poor performance and, as the shock home defeat to Northampton Saints continued to haunt them in their bid for a home quarter-final, it subdued a historic occasion.
The impact was felt 24 hours later when Saracens' bonus-point win over Edinburgh denied the northern province a home quarter-final. They will travel to London to take on the English side, with a home semi-final against Toulon or Leicester the prize.
Coach Mark Anscombe acknowledged the significance of the win, but his top priority is to get as many of his walking wounded back in harness long before the quarter-final in April.
"There are 13 or 14 unavailable for one reason or another. Two or three of them are only a couple of weeks away, so, hopefully, we'll be at full strength soon," he said.
"When you get to the play-off time of the year everyone wants to pick their best squad and we are no different in that. We'll see where we are and who is available in a couple of months time, but there is an opportunity now to regroup."
Ulster, without those heavyweights, needed each department to function on Saturday – but their line-out was a disaster zone and they coughed up six of their own balls, many of them inside the Castres '22' with the home side under the cosh.
Rory Best was the first to acknowledge that contributed to an unconvincing performance, but he took encouragement from the way they came back in the second half to win the match.
"I have been involved in Ulster teams and we have played very well in the first half and when a few things go badly for us in the second half, we roll over – that could have happened us here.
"It wasn't our best performance of the season by any stretch of the imagination, but you have to take your hats off to the boys for the way they went about their business in the second half," he said.
The swirling wind made it difficult for throwers and kickers, but Best admitted that they just did not fire on all cylinders.
"Everything was not just a couple of per cent off, we were probably 10 or 15pc off. I was allowing a bit much for the wind to bring it in, so they were crooked. Our concentration and some of our lifts weren't great, our movement was bad, the throws were horrendous. It puts a lot of pressure on you as a team if you can't win your line-out.
"The important thing for us is that we stood up. Even after losing the first line-out of the second half, we still competed. Sometimes you lose ones like that, but then to come back... we won a lot of crucial line-outs in the second half. We pride ourselves in our set-piece and when we get it right, we show what we can do," added Best.
Any notions of Castres being disinterested were quickly dispelled when centre Remi Lamerat sliced through for an eighth-minute try.
But Ulster just could not get on the front foot and an exchange of penalties between Pienaar and his South African compatriot Rory Kockott left it 8-6 at the break.
It got more worrying for Ulster after the restart, as Castres pinned them back inside their own half for most of the third quarter and with notions of a bonus point dead and buried, the real fear now was that Ulster wouldn't even win the match.
But they won good field possession from a dominant scrum and while the darting runs of Craig Gilroy, Paddy Wallace and Andrew Trimble didn't produce a chance of a try, they stretched the home defence and eventually Pienaar was presented with a kick in front of the posts to edge them in front with 16 minutes left.
He was narrowly short with a curling 35-metre kick into the teeth of the wind in the closing minutes – but Anscombe felt that the decision to go for the posts summed up a lot on the day.
"If he wasn't sure of the distance we should have put that in the corner and keep the pressure on them.
"One minute it looked as if it was going to go over, but it was a strong wind... but he is a quality player and he shut them out and did the job for us," said Anscombe.
One suspects they will not be the only angry words when the DVD of this one is dissected, but at the end of it all Ulster have finally won in France – even if it is not worth a song.
Castres – P Bernard; M Evans, S Bai (M Andreu 52), R Lamerat (P Bonnefond 63), M Garvey; R Tales, R Kockott (T Lacrampe 55); Y Forestier (S Taumoepeau 46), M Rallier (B Mach 62), A Peikrishvili (M Lazar 53); M Rolland, C Samson; M Babillot (J Bornman 56), P Faasalele, P Wannenburg (I Tekori 69).
Ulster – C Gilroy; A Trimble, D Cave, P Wallace, M Allen; R Pienaar, P Marshall (P Jackson 55); T Court, R Best, J Afoa; L Stevenson, N McComb; R Diack, C Henry, R Wilson (I Henderson 27).
Ref – N Owens (Wales).