Sorry, I'm not quite sure what you mean by 'scheduling' these posts? Basically we're in the final stages of page editing before launching a whole new website. So we're only working on pages, not posts, and the links are to other w/p pages on the same site.
However, I've re-visited both the new page which had this problem, and both an old page and made another new one, and the links work fine both for internal and external ones in these other pages. So... have put problem page content in a new page (without the image) and all good; and with image added it's OK too. But what I do remember happening was that when I first added the image to the problem page, it sat below the grey text area, and then the grey text area just kept extending with the added text - so maybe it was an issue with inserting the image first, before any text? or possibly with the new media manager, though it seems to work very well.
So, overall - problem solved by re-doing page: ie; a glitch must have somehow been introduced with the image or text originally, which is now OK. I realise this is v long-winded, but thought it might be useful if it is in fact a glitch with the new media manager.
Thanks for getting back to me so quickly. Cheers.