When I mirror multiple times in sketch mode, the mirror command seems to "remember" the mirror line. This is handy if I'm mirroring lots of entities across the ONE mirror line, but NOT if i'm using different mirror lines. So each time I want to change the mirror line, I have to press the Mirror command again, even though it is already selected. I noticed the other constraints don't have this problem (I can make a point coincident on a line, and then perform the same operation on a completing different line without having to repress the Coincident command), so I'm assuming it's either intended to be only used for one mirror line or it's a bug. Either why, it would be good to make the behaviour amongst the constraints operations consistent (i.e no memory effects)