Apparently, having too many items in your inventory can lead to a bug in the game that prevents you from combining the star charts with the metal bar later in the game. The items will disappear, but the new combined item won't be added to your inventory. This applies to the cracked version, and it is not confirmed whether the problem exists with other game variants.
According to rmcin329, the "problem is caused by having exactly 11 items before combining the star chart with the straight metal rod. 11 items makes for just barely enough to have 2 pages. The combined item you are supposed to get winds up disappearing completely when you try to combine them".