Desired bahaviour of $releasever when using --installroot

Hello list,
I am using the --installroot option and noticed something strange.
The baseurl in my .repo file contains both $releasever and $basearch.
When using with --installroot $releasever is translated to "Null" not 
the actual value while $basearch has no problems.
I couldn't find nothing in Bugzilla.

Is this intentionally or there is some bug?
Any advice is appreciated.

Thanks,
Alexander.