Character Space with Ruled Line

Hi everyone
I want to create a font for kids with English ruled lines, when I put those rule lines in character space, in order to have a continuous ruled line while typing and I test the font there is no problem, but after I install the font, when I type a space it will be a blank space with no ruled lines. How can I force character space type to be something other than blank?
Thx

It works for me when I test in LibreOffice.