Paste on Facebook only opens gallery

[Android Central Question]

If I copy text on my Samsung Galaxy Tab S3, I can generally paste it into other programs easily by the usual method. However, if I try to paste it into a Facebook status, whether it's a block of text or a url, the paste button will only open up my picture gallery, to allow me to paste in a picture. The only way round this I have found is to use the SwiftKey keyboard when I select and copy the text, so that it comes up in the preview on the keyboard. However, I an mostly using a Bluetooth keyboard, so I don't wish to use this method. Can anybody work out what is wrong?