Enchanting glitch

I was about to do a standard level 30 enchant when I realized that the enchant for level 30 was pretty bad. Thus, I placed some torches around the enchanting table to get the level down to level 27 or 28, and I selected the level 27 enchant on the item. However, ever since then, no matter how many or how few torches I place around the enchanting table, the standard enchant doesn't go down; it always remains the standard level 30 enchantment that is available at that time. I've broken and placed the enchanting table and bookshelves back down, I've re-logged, and this issue still persists.