directory search fails!(Seems to be a bug)

[ali hagigat]

The directory, 'di4', found by directory search algorithm, is not
considered for 'di2/preq2' of the rule, 'all5'. The steps to reproduce
the result has been written as three steps:

1)  makefile9:
-----------------------------------------------------
vpath preq1 di4
vpath di2/preq2 di3
all5:  preq1 di2/preq2
        @echo "kkkkkk"
preq1:
        @echo "llllllll"
di2/preq2:
        @echo "mmmmmmmm"
----------------------------------------------------

2) please type the following commands which build some
directories(di4,di3,di2) and files(preq1,preq2) :
[Figure 1]

mkdir di4
touch di4/preq1
touch di4/preq2
mkdir di4/di2
touch di4/di2/preq2
mkdir di3
mkdir di2
-----------------------------------------------------
Figure 1:

di4--->preq1
         preq2
         di2--->preq2
di3--->
di2--->
-----------------------------------------------------
3)  make -f makefile9
mmmmmmmm
kkkkkk