The code can switch from the GTalk v0.4 dialect to v0.3, but not the other way around. A session never starts out in v0.4 because the caps requirements for v0.3 are matched first. Gabble ought to start out in v0.3, but then switch to v0.4 if a "transport-info" packet is received with a "transport" node.
This might be causing Bug #29649.
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