I've managed to get into construction mode, I've got an engineer on EVA, he's got his little welding torch out, I can select a part but when I got to place it on the craft it won't attach anywhere. I'm spamming the left mouse button but it does absolutely nothing, no matter where I click, no matter how close or far the engineer is away. RMB gives the context menu as normal; QWEASD rotate the part as per VAB/SPH.
I just want to attach a part to a craft - how do I do that?!
ETA: This is in career mode for a mission, using a 3-star engineer - is it something daft like you have to have a 5-star engineer in order to do this?