Not a bug
Quoting this page:https://www.advanpix.com/2011/11/07/gauss-kronrod-quadrature-nodes-weights/
"If input parameters a and b are multiprecision type, then all subsequent calculations inside the function will be conducted with high precision,..."
Re: Matlab 2021a under Windows 10:
User-written subroutines are executed in quadruple precision (34 digits) regardless of number of digits possessed by arguments passed to the subroutine.
For example: If arg1 has 100-digit precision and is passed to subroutine1(arg1), then computations within subroutine1 will be performed in 34-digit precision unless the following statement appears inside:
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