make and .ORDER

[Aleksey Cheusov <cheusov%tut.by@localhost>]

Can anybody please explain point 2# and 3# shown below?
point 1# is clear. Here there is a loop in dependency and .ORDER. 
Point 4# is also clear.

Native make from NetBSD-5.1 works the same way.

      0 ~>cat ~/tmp/3.mk
      .PHONY: a b ab

      ab: a
      ab: b
      a: b

      .ifdef loop
      .ORDER: a b
      .else
      .ORDER: b a
      .endif

      a b:
              @echo $@

1#    0 ~>nbmake -f ~/tmp/3.mk -j 4 a loop=1
      `b' was not built (made 1, flags 2009, type 1010001)!
        `b' has .ORDER dependency against a (made 1, flags 1009, type 10001)

2#    1 ~>nbmake -f ~/tmp/3.mk -j 4 a       
      `b' was not built (made 0, flags 2009, type 1010001)!

3#    1 ~>nbmake -f ~/tmp/3.mk -j 4 ab 
      `b' was not built (made 0, flags 2009, type 1010001)!

4#    1 ~>nbmake -f ~/tmp/3.mk -j 4 b a
      --- b ---
      b
      --- a ---
      a

      0 ~>pkg_info -I nbmake
      nbmake-20101126     Portable (autoconf) version of NetBSD 'make' utility

      0 ~>

-- 
Best regards, Aleksey Cheusov.