in ch1, i found the letter, decoded it (+XP). I put it in a bag.
in ch2 i gain my equipment back, but notice that i have 1 sharkman letter in my inventory, undroppable. Didn't pay attention too much.
Later, i notice I have one in the bag and 1 in my inventory.
Both are undecoded.
I decypher one. (+XP)
The other remain coded.

I'm deciphering the second, to know if i still gain xp, a third time. YEs: +XP.
I'm quite sure it's not normal.