I successfully ran LTP 5 & 6 on my iPad2 last night, duplicating the entry for the day's flying. LTP6 has downloaded as a separate App, not modified LTP5.
Ah, I think my problem is that I got the iPad version after September, so even though it was LTP5 it was technically LTP6.0 and when the real LTP6 came out (LTP6.01) it updated the one I had. They did it that way so that people purchasing it for the first time close to the upgrade date got a free upgrade to v6.