After wasting more than one hour trying almost everything, finally I
discovered the stupid problem.

Look for "special character spaces" in fields: the spaces between words
or spaces at the beginning of empty fields. Then copy/paste one of
those "special spaces" and replace it by the normal space (when you use
the space bar) in all the document using "find and replace".

Also, remove the spaces in empty fields. Should work...

Nuno