asin(-sin(x)) simplifies to -asin(sin(x)); resimplifying that using expand(...,0,0) gives -x.
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The bug was in trigi.lisp; odd/even-function-reflect, which were constructing their result using
(neg `((,op simp) ,(neg x))))
which blocked the second simplification.
Corrected in trigi.lisp 1.26 to:
(neg (take (list op) (neg x))))