Intangibility: Has yet to be successfully developed, for most of the reasons given in the trope page (although I disagree on one major point: intangible objects can and probably should have mass; it’s the electromagnetic interaction they need to be lack in order to properly interpenetrate).
There is one prominent failure mode, however: muon metals, thanks to the Pauli Exclusion Principle, can pass through normal (electron-ic) matter as if it wasn’t even there, since electrons and muons do not mutually exclude. This makes life interesting if the magnetic couple necessary to hold the (muonic, due to the spectacular refractory properties of muon matter) magnetic nozzle of your torch drive in place fails, since you may well see said nozzle fly right through the rest of your ship and indeed you, impelled by the remaining coupled thrust. People tend to find this disturbing.
(Well, briefly, since a mere moment thereafter they tend to be preoccupied with the stern of their starship melting, vaporizing, and exploding, due to the ensuing catastrophic drive containment failure. And yet.)
Two things spring to mind… firstly, that muonic atom nuclei are still things that can interact with normal matter, so a dismounted drive shield’s progress through your ship won’t be unimpeded, and might conceivably be quite destructive. If there’s anything dense between the nose and tail of your ship (like a shadow shield made out of boring old matter because it doesn’t get that hot) it’ll probably hang up there.
Secondly, there’s nothing to stop you making a partially muonic atom (indeed, this has already been accomplished in real life with muonic helium), and such a material would be a useful thing to make the cold side of your drive shields with, for convenience of bonding to boring, normal matter.
(of course, such a thing might be precluded by whatever magic prevents the muons decaying; the hands are yours to wave, obviously!)
On further reflection, said drive shield will also be very, very hot… after all, if it were under 3000K you could just use tungsten instead of handwavium. It’ll probably also be quite heavy, and so have a lot of thermal mass. It won’t drift though ghostlike, so much as all-consuming-fireball-like