A button should be made that when pressed saves the currently shown block from being replaced.

[Apochrosi]

In the current version you can use the show block function to temporarily see most of chosen unicode blocks glyphs. When you press show for another block, the prior block is removed and replaced with the glyphs from the new block. Th only way to avoid this is to give a temporary glyph a texture, it will then stay even if the temporary block that is shown is swapped for another.