I recently had a view called "Catalog" in which I was trying to override the mini pager using the theme_views_mini_pager() theme function. The problem was that views was passing theme patterns into the theme function with the capital "C", such as:
The hooks variable array inside the theme() function contained "views_mini_pager__catalog" which means my theme override function was never getting called. I simply cloned the view and renamed it to something without a capital letter, and my theme override function began working just fine.
I am not sure if this is a bug in views or in Drupal core. It is a pretty specific bug that I doubt many users will ever run into, however I thought it was good to document the findings.
If you need to override the views mini panel pager, make sure to name your view in all lower case letters. I have only tested this in Views 6.x-2.16.