temporary function variables in user defined make functions not blanked out

[Noel Yap]

I've got the following makefile:

define reverse-list
  $(if $(strip $(1)), \
    $(call reverse-list,$(call pop-front,$(1)),$(firstword $(1)) $(2)), \
    $(2))
endef

good-wrapper = $(call reverse-list,$(2),)
bad-wrapper = $(call reverse-list,$(2))

.PHONY: all
all:
        echo $(call good-wrapper,,a o e u)
        echo $(call bad-wrapper,,a o e u)

with the following behaviour:

piias306 /ms/user/y/yapn/proj/aoeu 77$ gmake
u e o a
u e o a a o e u

Is this a bug, or an undocumented feature?

Thanks,
Noel
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