I think when you say "weird" you're probably asking if there is higher risk in 5 year notes as opposed to 3 year. There may or may not be. Great answer I know, but the reality is that P2P is still too young to have an exact answer for that. But I believe the higher interest rates on 5 year notes do compensate for that risk - that's just an opinion though.
I've been doing this for 19 months now, and have accumulated 41 charge-offs on 1400+ notes between LC and Prosper, but am still making a 15%+ return overall. At Prosper 56% of my money is in 3 year notes, 44% in 5 year notes. Of the 25 charge-offs there, only 4 are from 5 year notes with 21 being from 3 year notes. At Lending Club 36% (between 2 LC accounts) is in 3 year notes, and 64% in 5 year notes. I have 16 charge-offs at LC, 9 are from 5 year, 7 are from 3 year. So in my brief and limited experience in P2P lending, I don't see 5 year notes yet as riskier than 3. But of course that could change over time.