During the show and tell sequence near the end of the special, 5's hair strands are longer than the one he had during the party.
5 wears a red shirt and socks at the party but it changes to orange during the end of the musical number "Pigpen Hoedown".
During Snoopy's big dance in the disco, his shirt briefly disappears and reappears.
On Snoopy's way to the disco dance, the neighborhood background pans backwards, instead of forwards, as he walks.