This has happened to me 3 times now! I get a 15 min invoice from Bitpay and I immediately send a payment from Coinbase or Multibit, but the transactions never shows on the blockchain and the invoice expires. I search the transaction hash on the blockchain.info and I get this error "Sorry we could not find any blocks or transactions matching this hash". I then send a second payment from the wallet and the transactions show instantly on the blockchain!
Why is this is unreliable? Why do some transactions show immediately on the blockchain and other do not? It is VERY frustrating!
Sounds like a bug in MultiBit, but more details would be needed to know for sure.
If such a bug existed in the most recent version of MultiBit, I'd expect a lot more people to be complaining about it, so it sounds like you might be doing something unusual.