The crack is rarely spontaneous. It is usually the result of cumulative stress, thermal expansion, or manufacturing defects exacerbated by the constant pull and release of magnetic force.

Mix your joint compound to a creamy consistency (like peanut butter). Using the 4-inch knife, force compound deep into the V-groove. Immediately apply a strip of over the wet compound, then skim a thin layer over the tape, feathering the edges 2 inches beyond the crack. Let dry for 24 hours.

That being said, here's a review of Magnet Office:

: Developers often provide limited-time trial versions for professional evaluation.

Until Tuesday at 10:14 AM.

A professional will often use a (like Strait-Flex) and a setting-type compound that cures harder than air-dry joint compound. They may also recommend replacing the magnetic paint section with a steel-backed magnetic board.

Press around the crack with your thumb. If you feel any "bubbling" or movement, cut out that section of drywall paper until you reach firmly attached material. This prevents the crack from reappearing next week.