Hello Sukie -
We are not aware of any issues with our service that would cause Gallery Plus to be added to listings without it having been selected on a particular listing.
We did, however, recently enable the Optional eBay Gallery images by default on listings, so this feature (which is cost free on eBay US) is on when you go to create a new listing. If you do not wish to use the Optional eBay Gallery images, you can just deselect the checkbox for them when you have completed your listing and the Optional eBay Gallery images will not be utilized.
Please be aware that we have a feature request in to our Product Management team to have this available as a setting in the account preferences to be able to set this on or off by default as the result of a preference.
If you are encountering an issue where Gallery Plus is being added to your listings without your intent, please file a support case from under the Help tab of the site letting us know the details of your experience, an unmodified sample listing title and your browser and operating system information and we will be happy to look into it for you.
-Craig