If I understand you correctly, what you are seeing is expected behavior for Master Page items. They are visible on document pages, but not editable there.
They can be unlocked on the document pages (shift - command - click)
You should not put any text frames on the master except those for running headers and page numbers.
There are a few best-practice guidelines that many people agree on, but they are not rules that cannot be broken. If you choose to not follow the guidelines, you accept some loss of control over your document, so consider how you are working and choose what works best for you.
Most of the time, if you want something on every page (of the document, or just a range of pages) to be the same, put it on the master page and don't change it on the document page. If you want it to be different on a document page, maybe it should be made there, rather than on the master page. If you release a master object on a document page (by clicking on the object while holding Shift and Command), it will still respond to changes to the object on the master page as long as you don't change it on the document page. For example, if you move the item on the document page and then move the object on the master, all of the document page items will move except the one that you already moved. The same goes if you change the color, shape, rotation, etc., so the advantage you get by placing something on the master page is lessened if you release it on the document page, so maybe just creating it on the document page is a better choice. It's up to you.
Also, when View>Extras>Show frame Edges is selected and the page view is Normal you get some helpful cues regarding MP items vs. regular page items.
There is a distinct difference between a page items and master page items. Master page items have dotted frames:
On a document page that has the master page applied, a Master Page item that has not been overridden via Command-Shift-Click continues to have a dotted frame (left), overridden master page items and regular page items have a solid frame (center), and master page items that are protected from being overridden have no border (right).
You can return an overridden master page item to a master page item by selecting it and choosing Pages>Master Pages>Remove Selected Overrides. That's not an option if the selection is a page item or a detached master page item.