If your are looking for something to do, here is what I know about
bug #1726550 (also not(f[1](2)), "and"(f[1](2)), ...):
(%i1) is(f[1](2));
Maxima encountered a Lisp error: Error in PROGN [or a callee]: Bad plist
((1 DATA ...
mevalp2 calls isp (defined in db.lisp). And isp calls truep. Then
truep (or semant) gets stuck in an infinite (?) loop. Changing meval2 to
(defmfun mevalp2 (patevalled pred arg1 arg2)
(cond ((eq 'mequal pred) (like arg1 arg2))
((eq '$equal pred) (meqp arg1 arg2))
((eq 'mnotequal pred) (not (like arg1 arg2)))
((eq '$notequal pred) (mnqp arg1 arg2))
((eq 'mgreaterp pred) (mgrp arg1 arg2))
((eq 'mlessp pred) (mgrp arg2 arg1))
((eq 'mgeqp pred) (mgqp arg1 arg2))
((eq 'mleqp pred) (mgqp arg2 arg1))
(t patevalled)))
;;(t (isp (munformat patevalled)))))
keeps this bug from manifesting (I'm not proposing this as a fix).
Barton