Hi Ajay,
Unfortunately, I cannot reproduce this on a default installation of WordPress with the wp-mvc plugin running. So, the likely cause here is another third-party plugin that you are running that is interfering. You can try disabling plugins one-by-one until you find the cause.
In answer to your other questions, we are working on how best to embed wp-mvc in a self-contained plugin, but for now it must be run alongside any other plugins built on wp-mvc to get them to work.
It is very easy to create admins for new content, even without assigning them to a custom post type. See the documentation at https://wpmvc.org/ for more details.
I hope this helps point you in the right direction!
Best,
Robert