In the tech tree, there are assorted MechJeb 'parts' which serve only to indicate which new functions are unlocked by buying that tech. Actually purchasing these parts is not necessary; the functionality is unlocked simply by buying the associated tech. Yet the parts in question have unlock prices, making it very easy to waste money buying them, especially using the 'Buy All' button.

Either the function unlock system should be changed so you have to actually buy the relevant pseudo-part to get the new functionality, or the pseudo-parts should have their unlock cost changed to 0.