I'm trying to export a page from an indesign document where I have "linked text" from that same indesign document. When I copy and paste de page into a new indesign docuement, the linked data is lost. Is there a way to fix this? When there's a linked image, the link is also copied, but not the text... what's going on?
There's no malfunction there. The behavior you're seeing is by design.
By default, all placed images are links to the original, external image file.
When you Place and Link text, there is no objectively "external" file to reference in a universal sense. To maintain (or more accurately, establish) a link between documents, you must use Place and Link again.
So, to do what you describe; instead of copy/pasting the page content, select all and choose Place and Link. With the cursor loaded, switch to the other document and drop-click.