[yocto] Where to set preferred_version / preferred_provider

[kris duff]

Hello!
I am using webmin 1.620 on my image (a custom recipe in my own meta layer). When I have upgraded my yocto revision to dizzy, a new webmin version has appeared in the meta-openembedded layer (the version is 1.700) this version seems not to work (I am unable to start it using systemctl and when I try to add a webmin.service in a bbappend it fails).
I have tried to put the instruction PREFERRED_VERSION_webmin = "1.620" in my meta layer conf/layer.conf but I can't make it to work.
When I add PREFERRED_VERSION and trying to bitbake my image, I receive a message telling me that the image have to install 2 version of the same package. (probably because the package is present in multiple meta layer)
I also tried to add a version suffix in my image (webmin-1.620 or webmin_1.620 and I always get an error telling me that this package is not found.). Then I would like to try PREFERED_PROVIDER_ but I don't understand how this command should work with webmin.
For now, I have removed the webmin_1.700.bb file but, this is not a good solution.
Any idea ?
Thank you 
Kris
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