Characters sheathe their weapons to their backs or other places, but there's nothing there to hold those weapons in place. Often makes it seem like they have magnetic shoulder blades or similar.
The first video game about Magnetic shoulders was released on August 23, 2001.
This is mostly an intentional oversight on the matter, and players rarely if ever seem to care.
Also includes sheathing weapons to waist or other locations when there's seemingly nothing holding them there. Especially noticeable when the character is nude in that part of the body (e.g. bare upper body but weapons are sheathed on the back as if they had something there besides their skin to hold them there).