Happens on 1.14.6-1+b1 and some CVS HEAD version I have dated "Oct 26  2022":
  $ printf '%s\n' '.ds ABCD zupaninka 3' '.ie dABCD "\*[ABCD]".' '.el noabcd' | mandoc
  ()                                                                          ()
  
  "zupaninka 3".
  
                                                                              ()
  $ printf '%s\n' '.ie dABCD "\*[ABCD]".' '.el noabcd' | mandoc
  ()                                                                          ()
  
  "".
  
                                                                              ()

At least -Tlint also warns for this since it's using an undefined
variable. But it probably shouldn't since mandoc_roff(7) says
  • If the first character of condition is ‘d’, it evaluates to
    true if the rest of condition is the name of an existing user
    defined macro or string;