RTL stylesheets still load even when parent LTR ones are disabled in .info

This may be more of a documentation piece, but it really needs to be out there. There have been no core issues on it that I can find, nor do I see this practice documented anywhere.

Example:
system.menus-rtl.css still loads even if system.menus.css is disabled in .info file when viewing in rtl mode (tested using arabic).

adding..
stylesheets[all][] = system.menus-rtl.css
..to the .info file resolves this.

The good news is, the RTL's loading are not affected by this bug that took a long time to squash #967166: Content rendered via AJAX does not respect stylesheets removed in .info files

Steps to reproduce:

• Enable locale module
• Visit /admin/config/regional/language
• Click add language and select a RTL language (I chose Arabic)
• Set your chosen RTL language as the default, save and close the overlay
• Inspect any collapsed element and see that system.menus-rtl.css is loading

Screenshots to back up the find:

screenshot with only stylesheets[all][] = system.menus.css in .info (Stark):


screenshot with both files in .info (Stark):

stylesheets[all][] = system.menus.css
stylesheets[all][] = system.menus-rtl.css

This issue was originally discovered in the Zen issue queue (by me), just getting around to testing it in core.
#1617996: RTL files still load even when removed via .info file