make buildin function strings handling

[Incarnation Lee]

I am improving my codes which managed by gnu make recently. And I found a behavior of make buildin function when handling strings. I assume that this maybe for some specific situations. My OS is Ubuntu 12.04 and with gnu make v.3.81. Details list follow:
obj=a.o b.o c.o

define Test
tmp1=$(word 1, $$(obj))
endef
$(eval $(call Test))
tmp2=$(word 1,$(obj))

echo $(tmp1)
echo $(tmp2)

do make -n
and get the result 
a.o b.o c.o(tmp1)
a.o(tmp2)