Um, no, that just means it would be rated at 60 amps for 120 volts, but it's still 30 amps for 240 volts. Your breaker is defective or you didn't charge long enough. My in-laws have the same setup and unless I dial it down to 32 amps, it will blow the breaker eventually. At 40 amps, it took about 20 minutes.
Not quite. 30A is 30A is 30A. A breaker labeled 30A will permit only 30A to flow through any wire attached to the breaker.
On a 240V circuit, the power is supplied via two ungrounded conductors ("hot" relative to neutral). Because these are both ungrounded conductors, they must both be protected against overcurrent (return to the grounded conductor). This is why 240V breakers are dual-pole and double-wide -- each conductor is protected. The internals of these breakers are nearly the same as the internals of two stacked single-pole breakers. The handles are tied together so it will disconnect both conductors if one trips.
On a 120V circuit, the power is supplied via one ungrounded conductor ("hot") and the grounded conductor ("neutral"). Because the grounded conductor is 0V relative to ground, it does not need to be protected with overcurrent protection (fuse/breaker).
So it's not rated for 60A for 120V. If you were to use a double-pole breaker for a 120V circuit (by piping the neutral through the other side of the double-pole breaker), it would still limit the current to 30A - you wouldn't get 60A.
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The answer, I believe, lies in the fact that a 10-30 outlet is rated at 30amps PER POLE. Each wire and each breaker and each contact is rated for 30amps. Making it a 60amp outlet.
For the same reason I describe above, it's not a 60A outlet. In a circuit, you don't count power_in + power_out... there's only 30A flowing, whether it's between "hot 1" and "hot 2" (240V), or "hot 1" and "neutral" (120V).
Your breaker didn't trip because they can be overdrawn for periods of time. I mentioned the standard, above, which requires a breaker trip at 135% of load within 2 hours.
