Uncaught type error in CONCATENATE 'VECTOR with improper list argument

[Paul F. Dietz]

(lambda () (concatenate 'vector '(a . b)))

==>

The value
  B
is not of type
  LIST
   [Condition of type TYPE-ERROR]

Restarts:
 0: [ABORT] Exit debugger, returning to top level.

Backtrace:
  0: (SB-KERNEL:LIST-TO-VECTOR* (A . B) VECTOR)
  1: ((FLET SB-C::COERCE-CONSTANTS :IN "SYS:SRC;COMPILER;SEQTRAN.LISP") (#:G1) VECTOR)
  2: ((SB-C:DEFTRANSFORM CONCATENATE) #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::GLOBAL-VAR :%SOURCE-NAME CONCATENATE :TYPE #1=#<SB-KERNEL:FUN-TYPE #> :DEFINED-TYPE #1# :WHERE-FROM :DECLARED :KIND..
  3: (SB-C::IR1-TRANSFORM #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::GLOBAL-VAR :%SOURCE-NAME CONCATENATE :TYPE #1=#<SB-KERNEL:FUN-TYPE #> :DEFINED-TYPE #1# :WHERE-FROM :DECLARED :KIND :GLOBAL-FUN..