It's usually your fault, not the fault of the greenstuff. The sticking strength of greenstuff to plastic or metal isn't great, it's usually best to reinforce it with superglue, once the putty has cured, wherever possible. For larger items (especially wings) I'd advise using a pinvice to insert a paperclip into the item you're building on to provide added support and rigidity, which will also make sculpting much easier. It's much easier to sculpt the putty around the clip rather than insert the pin once sculpted, a) because of the rigidity and improved ease of sculpting and b) because it's a delicate task usuing a pin vice to drill into greenstuff.
So far with my Emperors Champion, all I need now is to do the sword, right pad motif, iron halo/rosarius, base and touch up the purity seal parchment a little, along with painting the holster and backpack and glueing them on. The helmet also needs touching up because I tried the eye glow tutorial inthe stickied threads, didn't have a proper glazing agent and relied upon watering it down and to cut it short botched the job impressively. I will however also be trying sourced lighting from the iron halo. Overall the armour I'm very please with, considering it's the first serious painting I've done in years, though the laurel wreath is very shoffy and the loin cloth has some extreme contrast going on which makes it very much an arm-distance-pleasant model.
The outside of the cloak on the Inquisitor scale arbites is just about done in a brown leather look that took a lot of washes of scorched earth over snakebite leather, with some later highlighting. So far I'm very pleased with it, though we'll have to wait and see how it all looks once the inside is painting purple. Other than that the model remains mostly white, except for where it's been blocked in where I plan to try NMM gold.
The mordheim warband has been cut off it's sprue, slightly converted and mostly glued together and onto bases (with superglue so that I can break them off to greenstuff on some cobbles when I get round to it). Other than that it's just the captain that I've undercoated and played around with a little.
Pictures to come when I can blag my dads camera.