Invalid post type.

When bulk editing default posts on the edit screen and you are filter by Tags, you will get an error message Invalid post type.

How to replicate the issue:
1. Go to Posts -> All Posts
2. Click on any Tag in your posts lists.
3. Select 2 to 3 posts.
4. Click on Bulk Actions -> Edit -> Apply
5. Select a new category to link to the posts being bulk edited.
6. Click on update.
7. Invalid post type and in the URL &post_type=Array

This seems to be an issue in the file: mec.php line 413 or main.php line 558.