My LO did something simlar for months--started around 8 or 9 months and continued until he was 13-14 months. At that point, the morning nap was getting him so well-rested that he wouldn't take a cat nap, but it wasnt' late enough to be his one nap, so we had to start doing a 20 minute am nap (usually in the car
), which we did until 18 months, and then he finally went to one nap.
At 8-9 months I tried the short am nap and it didn't work at all, so we stuck with long am nap and short pm nap for quite a while.
Bethany