If the sentence is taken literally, either interpretation could hold. However, for most readers or listeners, only the second interpretation is ever thought of. That is, all but a tiny fraction of auditors take the meaning to be

We believe X at present, and will continue to do so, until such time (if any) as X is disproved.

Under the second interpretation, there is no implication that X will or might happen, but such happening is not ruled out. The first interpretation, on the other hand, seems to require a belief that X is going to be proved wrong. But if you know or believe X will be proved wrong, it is willful perversity to meanwhile believe in it; so apparently the first interpretation is unlikely to ever be correct.

If the sentence is taken literally, either interpretation could hold. However, for most readers or listeners, only the second interpretation is ever thought of. That is, all but a tiny fraction of auditors take the meaning to be as below, where X denotes the thing in question which is not yet proved or disproved:

We believe X at present, and will continue to do so, until such time (if any) as X is disproved.

Under the second interpretation, there is no implication that X will or might be proved wrong, but such proof is not thought impossible. The first interpretation, on the other hand, seems to require belief that X will be proved wrong. But if you know or believe X will be proved wrong, it is willful perversity to meanwhile believe in it; so apparently the first interpretation is unlikely to ever be correct.

If the sentence is taken literally, either interpretation could hold. However, only the second interpretation ever occurs or will occur to most readers or listeners. That is, all but a tiny fraction take the meaning to be "we believe this, at present, and will continue to do so, until such time, if any, that it's disproved."

If the sentence is taken literally, either interpretation could hold. However, for most readers or listeners, only the second interpretation is ever thought of. That is, all but a tiny fraction of auditors take the meaning to be

We believe X at present, and will continue to do so, until such time (if any) as X is disproved.

Under the second interpretation, there is no implication that X will or might happen, but such happening is not ruled out. The first interpretation, on the other hand, seems to require a belief that X is going to be proved wrong. But if you know or believe X will be proved wrong, it is willful perversity to meanwhile believe in it; so apparently the first interpretation is unlikely to ever be correct.