According to the documentation of the CL library, it is allowed to have code like

(cl-check-type '(a b) proper-list)

where the undefined type symbol proper-list will be automatically interpreted as

and indeed it does work. However, after upgrading from Emacs 27.1 to 29.1, I am suddenly getting a compiler warning

Warning: Unknown type: proper-list

for such lines, unless I either rewrite it more verbosely as

(cl-check-type '(a b) (satisfies proper-list-p))

or provide an explicit type definition

(cl-deftype proper-list () '(satisfies proper-list-p))

Is anyone aware, if this is intended behavior?