What version of DW are you running?
If you aren't running the latest version, you should up date to it.
There may be a lag in use first heading if you have only recently updated from a DW version which did not have metadata. The first heading is retrieved from the page's metadata. For efficiency reasons, the current release of DW doesn't generate fresh metadata if its not available - when its looking for first headings.
In a wiki constructed wholly after metadata was added this should never cause a problem.
To get around the lag, spider your wiki. Viewing a page will generate its metadata so there will be a first heading available for search, index, backlinks etc. Spiders include software like HTTrack, WinHTTrack, wget and others.
Improvements have been made in this area in the development version of DW - there shouldn't be any lag. You can get hold of the development version by following the instructions at
http://wiki.splitbrain.org/wiki:development