Anytime you check off "Texture" in the Materials pallete, it will be transparent.
Apparently you must be starting your "new file" transparent instead of with a white or colored background.
If you don't want a transparent background, whenever you open a new file... uncheck "transparent" & select the color that you want to start with.
Or if your background is aready transparent, just add a solid white or colored background & then put your textured background on top of the solid one (in a different color) & then the blocks won't show through.
If you lay the exact same color of your solid & textured background together, the texture won't show up.