After setting the items per page to 200, the setting does not persist or is changed at seemingly random occurrences.
Rally does not have a global or persistent default value for the items per page setting. Because of this, the setting that controls the number of items per page can seem inconsistent because a number of actions can change this to a different value.
For example, if you go to the User Stories page and set the value to 200, but then choose a view, you will have that setting changed to whatever the view's setting is set to.
Additionally, the setting is per page, so if you set it to 200 on the User Stories page, that setting won't carry over to the Defects page.
Finally, any time you use the "Clear View" option from the Saved Views dropdown, the value will revert to 25 again.