IBM had a tradition of not allowing customers to fall down. JES3 took down a bank in Buffalo. Fortunately for the guilty a major snowstorm had shutdown the city for several days. IBM sent in SEs on snowmobiles.

COLT was even worse as it could throw a mainframe into an interrupt cascade. You had to press System Reset, then IPL and pick up the pieces of transactions. It took me a few months to identify where a register got mangled over an interrupt. This was pseudo reentrant code which I came to utterly despise.

I characterized the code as the result of student intern self abuse.

I spent several months flogging that dead horse until I changed jobs. There were later opportunities at other banks that saw COLT on my résumé that I refused.

In the current millennium, IBM has been serially fomenting payroll disasters with Phoenix as it's known in Canada (I don't know what it's called in Australia).