[CentOS] yum --allow-downgrade and versionlocking not working

with installed version 1.3.7 from rpmforge

yum --allow-downgrade update rrdtool-1.2.30-1.el5.rf
results in "no packages to update"

yum --allow-downgrade install rrdtool-1.2.30-1.el5.rf
says "already installed"

So, how am I supposed to use --allow-downgrade then?

I had to rpm -e --nodeps the newer packages to be able to install the 
older packages. Now I want to lock the package version. However, again, 
yum doesn't work as I read from documentation. After adding

rrdtool-1.2.30-1.el5.rf

perl-rrdtool-1.2.30-1.el5.rf

to versionlock.list I get:
Error: Package tuple ('rrdtool', 'i386', '0', '1.3.7', '1.el5.rf') could 
not be found in packagesack

where I can't find any fix for.

Interestingly, I'm also getting this error on a simple "yum update", that 
I haven't seen before:
Error: Package tuple ('perl-DBD-mysql', 'i386', '0', '4.011', '1.el5.rf') 
could not be found in packagesack

This package was removed quite some time ago the same way because 
downgrading didn't work. (This package wrongly obsoletes a base package.)

What's going on here?
Even yum clean all doesn't help.


Kai

-- 
Kai Schätzl, Berlin, Germany
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