This is quite baffling, though not uncommon.
1. Potential remission?
2. Maybe his previous dose was becoming too high and so his PMPS was low enough for you not to shoot, and then he went up a little as perhaps a normal fluctuation and maybe the old insulin wearing off, and many hours later the AMPS was lower because all insulin was out of his body so it was no longer bouncing? This may still result in higher numbers later though, and possibly (or not) a reduced dose?
3. Partial remission or the "sputtering pancreas" trying to produce its own insulin?