As the game progresses the game auto creates units like for example "the scout" or the "baron" which are offered as a new alternative to the one already possible to create. Such units are supposed to be generated based on the new improvements available (armors weapons etc...) and can be modified. Well, by modifying those units one notices that the armor they are given do not exist and are more powerful than what they are supposed to be, in fact by switching to an improved version of their armor, for example, it becomes impossible to switch back and reach the armor values and the cost offered by the computer. This is definitely a bug, since that feature would make useless the option "upgrade" which would only lead to units less powerful and/or more expensive.