Problem of 'yum groupremove': removal packages' sequence is random

Hi, all,

 There is a problem with 'yum groupremove' command. 

 When packages PA, PB, PC is depending on PP, and %preun/%postun of
PA,PB,PC are referring to files in PP, and all 4 packages are in one RPM
group, the 'yum groupremove <RPM group>' command will fail.

 I've tried to enabled requires, requires(pre), requires(post),
requires(preun), requires(post) in spec files and rebuilt all packages
PA, PB, PC, but that doesn't help neither.

 The regular 'rpm -e PA PB PC PP' command doesn't report any problems in
fact which probably sorts out the package removal sequence
automatically. But the 'yum groupremove <RPM group>' command fails. The
packages removal sequence of 'yum groupremove' is:

 1, PA;
 2, PP
 3, PB
 4, PC

 So PB and PC's %preun|%postun reports failure because they are
referring to files in PP which is already removed before!

 The Yum version is 3.0.5, which comes with Redhat/Centos 5.1. Thanks.

Please help.

--Guolin