Hyperlink pathnames changed

[Oldsilver]

Hyperlink path changed:
In Word for Mac 2011 I can create a file, include a hyperlink to another file (e.g. a jpg pic), select Save as Web Page (it saves with a .htm extension). If I then go to that saved file and open it, my default browser opens the file, I click the hyperlink, and the required (jpg) file opens.
Then I go back to Word and re-open the file, edit it anywhere and save it again. When I then go to open it in my browser, the link doesn’t work: its pathname has been altered in one of two ways. Either 1) one or more forward slashes has been changed to a full colon, or 2) spaces in the pathname which are normally coded as “%20” have been changed to “%252520”. In either case, naturally the link no longer works. These changes can even be seen after saving but before closing the Word file, by viewing the file using View/HTML Source.
How do I prevent Word from changing pathnames in hyperlinks? Note, this problem is not related to any confusion or whatever with relative or absolute hyperlinks.