Unless specified, sequence functions must output a string of the same type as the input

src/CHANGELOG

@@ -124,6 +124,9 @@ ECL 1.0:
  - Following functions fixed to work with Unicode strings: EQUAL, EQUALP,
    PARSE-INTEGER.
 
+ - Most functions dealing with sequences (REMOVE, DELETE, etc) would
+   output a STRING even if the input was a BASE-STRING.
+
 * Other visible changes:
 
  - EXT:PROCESS-COMMAND-ARGS now allows for a default rule.

src/lsp/seqlib.lsp

@@ -16,6 +16,7 @@
 (defun seqtype (sequence)
   (declare (si::c-local))
   (cond ((listp sequence) 'list)
+	((base-string-p sequence) 'base-string)
         ((stringp sequence) 'string)
         ((bit-vector-p sequence) 'bit-vector)
         ((vectorp sequence) (list 'vector (array-element-type sequence)))