CentOS 7.1 was released on 31, March 2015. It ships with "httpd-2.4.6-31.el7.x86_64.rpm". As Virtualmin customizes HTTPD it needs to be recompiled to be compatible. The package fixes two security issues, several bugs, and adds various enhancements.
Would it be possible for you to recompile HTTPD from the updated packages?