The plugin’s default behavior is to add the buttons using the_content filter. Because it’s one of the most generic filters available, it gets used a lot. My guess would be that there is another function, plugin, or some kind of code, also editing the_content on pages, but not on posts, which is maybe conflicting with this plugin. That’s just a guess–it’s also possible that the buttons are being output but hidden somehow, due to some CSS or something which is preventing them from showing. If you can provide a link to an affected page, I can try to see if I can tell what might be going on, although if they’re not being output at all, it’s less likely.
If you can also tell me what location settings you have enabled (for both posts and pages), that would also be helpful.
If your theme provides any other filters or hooks around your content, it may be preferable to update the button locations using code (example in the FAQ), as a more specific filter/hook may reduce the possibility of conflicts.
