I'm constantly updating to the latest releases of wikit, so I don't know,
when and with which release exactly the bug was "introduced"... We mention the
following phenomen: References to existing pages (observed with WIKITOOL) fall back
to state of new, empty ones (the page content, however, is available in the database).
It seems that this happens to pages with MULTIPLE BLANKS in the PAGE TITLE. There
must be some changes to the handling of page titles some times ago (perhaps "2003-06-20
jcw * format.tcl: get rid of extraneous spaces when creating page titles", see
change log) which lead to this unexpected and unwanted result! The page titles
of already-created pages remain unchanged (that is, with multiple blanks within them),
but references to them appear with only single blanks on the screen.- Any ideas?

This is an onfortunate side-effect of the blanks-handling changes, I agree.
The way to resolve this is to go to a page with a title with such spaces in
it (by page number, you'll have to use search), and then make some small change
to the page and save it again. This should restore links for that page.