I think I found a bug - I bought some sells on the Derium Black Market. After a few seconds my Browser crashed and after reloading the game I don't have the spent Derium nor the cells anymore...
Hidden achievements (because I couldn't find any help on it...):
In general you have to search for a small color change - mostly grey.
Freebie: Just click the achievement.
In Construction: Search in the sand next to the Level Box, slightly higher than the (buy all) button.
In Explorer: Search in the sand left to the workers box on the left bottom. It's the height of the grey line, dividing the workers in 3 and 3.
In Dungeon: Search in the Stats Box in the right bottom corner. Its at the height of "increased xp". So just go to the left from the text and click a few times.
In Crafting: Search on the x-axis between the two upgrade columns. From there go up till you reach the black bar between the upgrades box and the level box.
In Merchant: Search in the level boxes left top corner. It's at the height of the line "Merchant stats".
 "Idle Pins"){kind=icon}
 "Midas' Gold"){kind=icon}
 "Idle Conqueror 3.1"){kind=icon}