French electro swing group Caravan Palace pulled out of last night's event in Glasgow over an apparent disagreement over travelling arrangements, claiming online the festival had been "unprofessional".
However, festival director Donald Shaw, who is also a musician and producer in Capercaillie, hit back, branding the band's no-show as "insane". He said: "I have never seen anything like it. Booking their flights was a complicated process but by Tuesday this week we had it organised, but they told us they were not coming. It's insane.
"As a musician, there is no way you let people down. It is one of the strangest things I have seen.
"Also as a musician, when there have been issues, I have always been of the opinion you say OK, let's play first, and have the argument afterwards. It is so disappointing and I am so sad they let their fans down."
Initial seats on flights to Scotland for the band had been booked, but then the band, who were due to play at the O2 ABC1, said they needed additional seats on their plane for instruments.
This was finally agreed with British Airways, Mr Shaw said, but the band insisted on confirmation by a deadline on Tuesday, two days before the concert.
"There was no question of us letting them down," he said.
On his Twitter feed he also said: "Absolutely gutted and dismayed at the attitude of Caravan Palace resulting in their cancelled show tonight, after months of bigging them up."
On their Facebook page the band said, in comments now apparently deleted: "Glasgow: due to our local bookers we will not play tomorrow. The show is cancelled. They have done b******* with our flight reservations and just woke up some hours ago ... too late of course.
"Maybe these guys really thought a vibraphone can be a hand luggage in the aircraft ... Or maybe the double bass can fit in my toilet bag!!! please ... We are so sorry about that and really angry to not be there."
A statement from the festival said: "Caravan Palace will no longer be appearing due to a breach of their contract - this situation was outwith the festival's control and box office is in the process of informing all patrons and their tickets will be refunded."
The band added on their Facebook page: "Two days ago, the flight tickets and extra seats were still not reserved, whereas tickets sales for the concert went fine, a concert planned months ago - for us, it's not normal, and really unprofessional."
Celtic Connections responded on Facebook: "At the time of writing, Caravan Palace have a fully booked flight schedule and baggage allowance with British Airways. All requests by the band have been met including additional seats which we have documentation to prove.
"There is no reason why this event cannot go ahead - and we have also offered extra help to get the band to the airport in time."