Thanks for reply. I think I know why.  When I put my RedeemScript in your area to construct the transaction, it shows me the three inputs, but the numbers are mixed up.
For example, the first one you listed from the decode transaction section is: 3fbd...120a   but is listed like this in the construct transaction section: 0a12...bd3f.
It looks like the 8 bit groupings are grouped together, but in some sort of reverse order (0a is at the start in one, and at the end in the other).
Correct me if I'm wrong, but it looks like (to me) there is an error somewhere in your code that flipped the txid's. ?
Is this a little-endian/big-endian thing?
I'm not sure why it would have worked for 2-of-3 but now for 3-of-5 it's being encoded differently?
-Luc

The same thing is happening to me -   the 3-of-5 isn't working.  I had a 2-of-3 work just fine this morning, but this afternoon, there is no way to get the 3-of-5 to work.  Is coinbin not coding the transactions correctly? (Tried with blockchain.info to push too)
Is my money lost for ever??? (  Thanks coinb.in...)  I hope that is not the case...
Thanks,
-Luc