Double colon rules fail to run in parallel mode

[grischka]

The below makefile snippet works as supposed in single-job mode, however in parallel mode under certain timing circumstances although it makes the prerequisites for each of the rules, it then decides not to run the commands, for the most part.

all rev: xyz.lib
    @echo - in $<:
    @cat $<
    @rm -f xyz.*
xyz.lib:: xyz.1.o
    echo - $^ >> $@
xyz.lib:: xyz.2.o
    echo - $^ >> $@
xyz.lib:: xyz.3.o
    echo - $^ >> $@
xyz.%.o:
    sleep $N
    echo hi > $@
R1 = 3
R2 = 2
R3 = 1
all: N=$*
rev: N=$(R$*)

$ make -j3 rev
sleep 3
sleep 2
sleep 1
echo hi > xyz.3.o
echo hi > xyz.2.o
echo hi > xyz.1.o
echo - xyz.1.o >> xyz.lib
- in xyz.lib:
- xyz.1.o