Description of problem:
The installation of buildroot failed, see: http://koji.fedoraproject.org/koji/getfile?taskID=3149029&name=root.log
There were missing requirements, but build phase started, see: http://koji.fedoraproject.org/koji/getfile?taskID=3149029&name=build.log

I'd like to point out that this bug is serious. Imagine, that you have package in C, which is checking by configure installed packages. In buildroot they are missing, but install could be successful because configure detect available packages and use available. Therefore you can have in specfile --with-selinux, but build could be done without SElinux support. 

Version-Release number of selected component (if applicable):
mock-1.10.0, but mock-1.1.11 doesn't have it fixed in changelog

How reproducible:
Add fake requirement in your package.

Steps to Reproduce:
1. into your package add Require: somethingreallystrange
2. build your package in koji
3. see this issue
  
Actual results:
Fail after build phase.

Expected results:
Fail after buildroot phase.

Additional info:
Could it be also bug in yum?