I just tried those steps 5 times and had 5 successful results. Perhaps rebuilding the database on your iPhone might help. From Safari on your iPhone, visit
http://people.omnigroup.com/kc/Debug...dDatabase.html and tap on the link there.
You might also consider doing the same thing on this page, first, if you're willing to let the Omni support people have a copy of your database:
http://people.omnigroup.com/kc/Debug...lDatabase.html
If the rebuild fixes the problem, the old database might provide some clues as to what was wrong.