Drop down Item - Link

Strange thing just happened while updating the Link of several Drop Down Items, upon saving the page the link goes from mypage.php?id=1 to just ?id=1

No matter what I do I can’t get the mypage.php to remain.

If I ‘save as’ the page it retains the full url and its the only page in several I’ve just worked on that won’t do as its meant to!

Any ideas anyone as to why?

Thanks
CK