I am very happy to announce a solution to the Movable Type bug that causes the creation of duplicate pages ending in "...name_1.php". If you are curious you can check out the thread in the Movable Type forums where the problem was reported and eventually solved. The following is the final post by the Six Apart Software Engineer Brad Choate:

Thanks DWD, the preview step is definitely the problem. This has been fixed for the next update/release.

You can sort of patch this one yourself by adding this in the form found in the tmpl/cms/edit_entry.tmpl file. Find this line:

CODE
[input type="hidden" name="id" value="[TMPL_VAR NAME=ID]" /]

and put this under it:

CODE
[input type="hidden" name="basename" value="[TMPL_VAR NAME=BASENAME]" /]

That will pass through the existing basename value to the preview step properly, so MT won't reassign it.

If you don't want to edit your templates, another workaround is to choose "Re-edit this Entry" after doing a preview and then save from the edit entry form itself. Another alternative is to use any of the weblog posting clients like Zempt or Ecto or w.Bloggar, etc.