There are two ways that you can get pages to change without actually pressing a Page button.
The first is Auto Page Select. This is a global setting. When turned on, each preset will select a default page when the preset is loaded. You can choose which page this is using the Show Page parameter in each preset. If Auto Page Select is turned on, make sure that Show Page is set correctly for every preset. You can also set Show Page to "Same" which doesn't change the page when loading that preset.
IA buttons that include the System / Page action also can cause unexpected page changes unless they're set up correctly. An IA button will of course trigger when you press it, but can also trigger automatically on preset change, depending on your button settings. We recommend turning off all checkboxes on the button except for the Momentary checkbox, which should be turned on. This will cause the IA page button to only trigger when pressed (and not during a preset change), and the button will not stay lit after it's pressed. This makes the button behavior correct for a button that changes pages.