The attached file is a minimized version of an official snippet.
If run as version 2.25.*0* it compiles perfectly.
If run as version 2.25.*1* it fails.
\version "2.25.1"
#(define-markup-command (on-color layout props color arg) (color? markup?)
(let* ((stencil (interpret-markup layout props arg))
(X-ext (ly:stencil-extent stencil X))
(Y-ext (ly:stencil-extent stencil Y)))
(ly:stencil-add (ly:make-stencil
(list 'color color
(ly:stencil-expr (ly:round-filled-box X-ext Y-ext 0))
X-ext Y-ext)) stencil)))
{ c''2 ^\markup { \on-color #green "pure" } s }