By default in the category chooser at the edit post screen wordpress displays the selected categories on top of the others, i find that extremely annoying and i would like to disable the feature even if i need a hack for this.
If I got this right, you need this plugin: Category Checklist Tree.
On the post editing screen, after saving a post, you will notice that the checked categories are displayed on top, breaking the category hierarchy. This plugin removes that "feature".
Additionally, it automatically scrolls to the first checked category.
Works with custom taxonomies too.