I just remembered another fun rule oversight (more of a quirk than a dysfunctional rule, but still humorous):

1) Fighty McFighterson straps on his full plate and goes out to slay evil.
2) Wizzo McEvilwizardington casts Sleep on poor Fighty, who fails his save and falls asleep.
3) Wizzo McGoodwizardington kills Wizzo McEvilwizardington (since we all know that it takes a Wizard to beat a Wizard) before he can finish off Fighty.
4) Fighty wakes up a round or two later and goes about the rest of his adventuring day no worse for the wear.
5) Tomorrow, Fighty is fatigued, thanks to the rule that says that "A character without Endurance who sleeps in medium or heavy armor is automatically fatigued the next day."