prerequisites of targets are not made?|?

[Alessandro Vesely]

Hi,
is that a bug or a feature?
I have a makefile like this:

-----8<----
all: all_targets

%.u:
        touch $@

an.u: source1
comp1: an.u
an.u: comp2
another.u: source2
comp2: another.u

all_targets:  an.u another.u
-----8<----
Actually, the middle part is a generated dependency that gets included
at that point. The idea was that a missing comp2 should have triggered
the making of another.u, instead, given the following files

   Makefile   an.u       another.u  comp1      source1    source2

make says that...

     Prerequisite `source1' is older than target `an.u'.
     Prerequisite `comp2' of target `an.u' does not exist.
    Must remake target `an.u'.
touch an.u

Thus, it always remakes an.u an never another.u.

Is this a bug?
Otherwise, why does it make an.u even if a prerequisite is missing?

Any help?
TIA
Ale