Four prison guards have been disciplined after they forgot to switch off a loudspeaker system and began criticising inmates who overheard their remarks.
The officers accidentally left a microphone on and used "derogatory language" about some of the prisoners.
Inmates complained about the guards' behaviour following the incident at HMP Channings Wood in Devon.
The Independent Monitoring Board (IMB) said the jail's deputy governor had carried out an investigation which found the inmates' allegations were "largely substantiated".
The guards made the apparently unintentional broadcast while they were in an office in the prison's LB2 wing - which is a "good behaviour" part of the jail housing 110 "enhanced status" inmates.
A report by the IMB said a "high number" of complaints had been sent in by prisoners "about the behaviour of a small number of officers" between October and November 2022.
The report added: "An incident [in October 2022] on an enhanced block (LB2) was brought to the board's attention.
"Prisoners had overheard what they claimed was the use of derogatory language about them after a microphone in the wing office had been left live.
"The deputy governor conducted a formal investigation and found that the events described by prisoners were largely substantiated.
"Disciplinary action followed against four officers."
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The report said the board "generally observed positive relations between prisoners and staff" but in some cases prisoners reported "it was more common to have bad staff" with "poor communication, a perceived lack of care, compassion and understanding".
It added: "It may be that staff shortages and frequent redeployments of wing staff to other locations make it harder to establish and maintain relationships. This also applies to key work."
A Prison Service spokesperson told Sky News: "This was a rare incident and appropriate disciplinary action was followed against those involved."