I think that this has been resolved in the current trunk build, but if it hasn’t it should be. You can use the Doc Manager module to bulk-set publish dates on a variety of pages.
Hmmm ... maybe clearing the cache would do the trick after changing all those since the cache doesn’t know about them and apparently the Doc Manager doesn’t clear the cache for the affected pages.

Refresh site
174 documents were published.
138 documents were unpublished.
Cache: Found 3 files in cache directory and deleted 0 cache files.
New cache files will be created when pages are requested.