I just realized this was implemented :)
And got first bug with it too ;)
Ending a Wiki page with (respect line break)
results in the value of %varname% to display on the
first line, and on the second a blank field even
without clicking to edit. It looks like it's not
possible to edit the variable when the bug occurs.
It's not 100% reproducable (probably that there are
other conditions necessary) but I got it both on my own
Tiki using day-fresh CVS and on tw.o also quite fresh
(see Sandbox's bottom maybe :p).
Here, the line after %varname% contains three spaces,
but I suppose other content could trigger it too.