Does the same behavior occur if instead of clicking on the "add page" icon you drag a new page into the document by "grabbing" either the "None" page icon or one of the Master Pages icons from the top of the Pages Panel and moving it into the document pages area of the Pages Panel? Does it happen if you use the Insert Pages option from the Pages Panel pull-down menu or from using Layout>Pages>Add (or insert) Pages?
If it is a problem with the Pages Panel itself you may be able to solve it by trashing your InDesign cache files. This is not the same as trashing preferences but it can be helpful in solving interface problems.
To do so:
For Macintosh Users: The User Library folder in which InDesign’s cache files are stored is hidden by default on most Macintoshes. To access it make sure that InDesign is closed and click on the desktop to launch a Finder Window (Command-N). With this window in column view follow the path User>Home folder (it’s the folder with an icon that looks like a house—it may have the user’s name rather than “Home”) and click on the Home folder. With the Option Key pressed choose Library from the Finder Go Menu. “Library” will now appear within the Home folder. Within the Library folder find the “Caches” folder. Within the Caches folder find and delete the entire folder “Adobe InDesign”. I find that deleting the InDesign cache folder completely leads to a lasting change.
For Windows Users: On Windows 7 and above the caches files are hidden. To find them go to the Control Panel and open Folder Options and then click the View tab. Then select “Show hidden files and folders” or “Show hidden files, folders or drive options” in Advanced Settings. Then delete (or rename) the folder at the end of this path: C:\Users\[User Name]\AppData\Local\Adobe\InDesign\Version [#]\<Language>\Cache.