This included abusive behaviour towards passengers, failing to follow bus routes, erratic driving and failing to keep both hands on the steering wheel.
However, Mr Keepa's driving was not "generally regarded as being a danger to other road users", the Employment Court ruling on the dispute said.
In May 2012, Go Bus regional manager Ashley Burton observed on three separate occasions Mr Keepa was driving with one hand on the steering wheel.
He reminded Mr Keepa on a daily basis to keep two hands on the steering wheel when driving, he said.
However, in the same month, Mr Keepa "immediately became aggressive and accused Mr Burton of picking on him", the court heard.
He then left his office and walked towards his bus to begin his shift. When Mr Burton followed him, Mr Keepa called him an "a**hole".
Mr Burton was concerned with Mr Keepa's "agitated and angry" state, so Mr Keepa was advised to spend time with a driver trainer. Further assessments by the driver trainer in July and August 2012 revealed "unacceptable behaviour towards passengers and a failure in driving standards".
The report also stated Mr Keepa was continuously failing to keep both hands on the steering wheel.
Mr Keepa also refused offers for further training and to discuss the matter with Mr Burton, which the company categorised as a serious misconduct, the Employment Court heard.
A disciplinary meeting took place in August 2012 in which Mr Keepa and his union delegate Bruce Graham proposed that Mr Keepa hand in his resignation, rather than have his employment terminated.
An agreement was made that Mr Keepa would sign a letter of resignation, if his employment record showed he resigned instead of being dismissed, so as not to prejudice his future employment prospects.
Judge Mark Perkins concluded Mr Burton was patient when working through Mr Keepa's driving ability, "often in trying circumstances", during his time as a bus driver.
"Mr Burton was meticulous in notifying the allegations... The process was conducted in a cautious manner," he said in his ruling.
Judge Perkins also stated it was clear one of the possible outcomes from the hearing was dismissal and it should have been clear to Mr Keepa or his representative Mr Graham.
Mr Keepa "gained a significant advantage from being allowed to resign rather than being dismissed insofar as any future employment prospects were concerned", Judge Perkins said.
The Employment court ruled in favour of the ERA decision, and ordered Mr Keepa to pay $3500 towards legal costs as originally determined by the authority.
