XOR with fractional DECIMAL operand: both XOR and NOT(XOR) return 1

Summary

XOR with fractional DECIMAL operand: both XOR and NOT(XOR) return 1

How to repeat

SELECT (-0.01) XOR 1 AS xor_result,

       NOT ((-0.01) XOR 1) AS not_xor;

Actual result on 12.2.2-MariaDB-ubu2404:

+------------+----------+

| xor_result | not_xor  |

+------------+----------+

|          1 |        1 |

+------------+----------+

Expected: xor_result = 0, not_xor = 1 (verified on MySQL 9.6.0).
Per MariaDB documentation, XOR "evaluates to 1 if an odd number of
operands is nonzero" — both -0.01 and 1 are nonzero, so the result
must be 0.

Also reproducible with runtime values, so it is not limited to
constant folding:

CREATE TABLE t(d DECIMAL(10,2));

INSERT INTO t VALUES (-0.01);

SELECT d XOR 1 AS x, NOT (d XOR 1) AS nx FROM t;

DROP TABLE t;

Pure integer operands and zero-valued DECIMALs behave correctly.

Analysis

Regardless of how a fractional DECIMAL is coerced to boolean,
NOT must invert the value of its operand. Returning xor_result = 1
and not_xor = 1 simultaneously is internally inconsistent.
The misbehavior appears specific to fractional DECIMAL operands
(e.g. -0.01 XOR '1' with a string literal reproduces as well).

Environment

MariaDB 12.2.2-MariaDB-ubu2404 (official Docker image), x86_64,
default configuration.