The underscore and the height of rows in the grid results

I use in windows 7 x64 PgAdmin
Version: 1.20.0

In the options Query tool -> Query editor : Font - "Courier New, 9"
In the window "Execute arbitrary SQL queries" write
select * from pg_class where relname like 'pg_%' limit 10
after F5 in grid results we see in the column "relname" text without
underscore.
If the row height to increase, we will see an underscore in its name.
If the font is changed to - "Courier New, 10" we will see an underscore.

Question: how to make the original line height was greater (for font -
"Courier New, 9")?

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Yours faithfully, Sergey Grinko
Email: sergey(dot)grinko(at)gmail(dot)com