There are photo stream settings in Aperture Preferences that control whether photo stream photos get automatically imported into Aperture. If enabled, Aperture automatically imports new photos from the photo stream to a monthly project (Its a project, not an album). Once imported into this project, what you do in the actual photo stream doesn't affect what's in the project. And changes you make in the project don't affect what's in the photo stream.
If you want changes you made in the project to appear in photo stream so you can see it on other devices, you must copy those photos manually back to photo stream. To do this use the Share menu or right click the photo and choose Share->Photo Stream.
Nothing affects what's in the photo stream except manually deleting photos (from within Aperture or your iOS devices) or automatically deleting photos either by exceeding the 1000 photo stream limit or 30 day limit.
Remember, the actual photo stream that shows in Aperture is totally separate from any monthly project that Aperture automatically creates with photos imported from photo stream.
Here are some support articles you may want to read, Jon:
And if you want to use shared Photo Streams: