In the early PC days we suspected them a lot given how manually writting Assembly was still much better, in many cases.
I found out a bug on Turbo Pascal 6, where if you declare a variable with the same name as the function name, then the result was random garbage.
For those that don't know Pascal, the function name has to be assigned for the result value, so if a local variable with the same name is possible, then you cannot set the return value.
(* In Turbo Pascal 6 this would compile *)
function Square(num: Integer): Integer;
var
Square: Integer;
begin
Square := num * num; (* Here the local variable gets used instead *)
end;
succ(seg(x)) and pred(seg(x)) turned out to be equivalent of just seg(x) in TP6.
Earlier versions of Turbo Pascal (and Poly Pascal) generated poor code for "... + 1" but better code with succ(...) and doing memory access via memw[s:o] was common for speed for certain kinds of code. Allocating whatever size you needed + 16 guaranteed you had allocated enough to have paragraph aligned allocation (16 instead of 15 so you could just use the segment + 1).
I think it took a day or two to find this bug in some text-mode windowing code I'd written.
I found out a bug on Turbo Pascal 6, where if you declare a variable with the same name as the function name, then the result was random garbage.
For those that don't know Pascal, the function name has to be assigned for the result value, so if a local variable with the same name is possible, then you cannot set the return value.
Something like this https://godbolt.org/z/s6srhTW66