On page http://www.pgadmin.org/docs/1.20/editgrid.html
there is a paragraph:
If you want pgAdmin III to write an empty string to the table, you enter the
special string ‘’ (two single quotes) in the field. If you want to write a
string containing solely two single quotes to the table, you need to escape
these quotes, by typing ‘’
As I can guess the last symbols of paragraph should be \'\' or something. But
not ''.
As I can guess it can be a result of convertation error, where \ were lost for
some reason.
May be it is not so difficult to fix it. So I do report it.