A complainant alerted the media regulator to comments made on the music and speech station, owned by Bauer Media, during its Breakfast Show on October 31, 2012.
In an interview with The Wanted, a presenter referred to band member Siva Kaneswaran's phobia about polka dots.
"Polka dots, what the hell? Are you... gay or something? You're scared of polka dots?!" the female presenter said.
Bauer Media said that the station's programme director responded to the comment by calling the team into a meeting, at which they accepted that "the comment made by the presenter could be construed as being derogatory towards homosexual people".
The firm said that the presenter was "extremely apologetic and in no way set out to deliberately promote certain negative stereotypes based on sexual orientation".
Instead, the remark was a "throwaway comment made without due thought", and she "completely understands the reason it may cause offence".
Bauer said that the situation was just an "error of judgement" and it has reminded staff not to let it happen again in future.
Ofcom accepted that the remark "Are you... gay or something?" was an "off-the-cuff put-down" during a lighthearted discussion.
However, it was concerned that the reference "could have reasonably been interpreted by listeners as promoting certain negative stereotypes based on sexual orientation, namely that homosexual people were more likely to be irrational or weak".
Ofcom noted the actions taken by Bauer Media but "concluded that in this instance... the licensee did not apply generally accepted standards".
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