Is it normal that the areas that you explored in a previous game session gets wiped when you reload the game?
It is quite aggravating when you explore for a few hours then decide to take a break and do something else only to find out it will be lost when you reopen the game.
Is there a fix?
IT’s a known bug that happens from time to time, though I don’t know exactly if we’ve nailed down what is causing it yet.
Okay 
I also noticed that the traps i set and deep holes i dig around my shelter also dissapear :s
I believe one potential cause people have been claiming that causes this is a problem with autosave, namely that sometimes autosave doesn’t completely save everything, thus resulting in their loss when the game is restarted.
Autosave NEVER saves everything. It’s not in the code. Someone may want to look at that. I don’t know if it’s a design compromise or someone simply overlooked it (hard to believe someone would write it to call save() without knowing what save() does exactly), but autosave() only calls save() and not save_maps(). Compromise or not, it should probably be changed since tons of people are getting all pissy about their autosaves getting “corrupted” because they’re not full saves.
I think it’s a problem with saving in general, not just autosave, because I turned off autosave and it’s still reverting the map back to unexplored whenever I load my character.