The furore it caused has brought consternation from a number of opposing managers and the media with the EFL writing to the club to ask for their observations on the matter.
In light of this there could now be a fear David Wagner may be compelled to play what is seen as the German head coach's more 'traditional' side to placate those unhappy.
Despite conceding twice, keeper Coleman was a bright spot in the defeat at St Andrew's, commanding his area well throughout and saving a first-half penalty from Lukas Jutkiewicz.
It was the 19th appearance of the season for the 30-year-old but the first in central defence - where Wagner was delighted at his display against the Blues.
Speaking after the game at Birmingham, the German boss said: “This was another change we did today, in terms of position, because we wanted to see him in the centre-back position as he hasn't played there this season.
“It was great to see how quickly he adapted to it and I think he played a good game.
“I think it was important for him to have a feeling for this position.
“Martin Cranie at centre-back and Joel Coleman in goal were two positives from the game going forward to the Play-Offs.”
A downside to last weekend's loss was the injury to Philip Billing – one which looks to have ruled the Danish midfielder out for the rest of the season.
And with Regan Booty on the bench last weekend, Wagner did not rule out the possibility of the youngster making his first-team debut against Cardiff City.
“We will see, why not?”, Wagner said. “We will see how the training this week goes and how the players rested are.
“Then we will make the decision who will be in the starting 11 and who will be in the matchday squad.”