Your vine probably got too dried out. Leaves can be expendable to many plants and they will shed them when they're stressed. Not to worry. Cut back the vine to live wood and keep watering regularly. Check to see if it's rootbound and either needs a root pruning or a 2" larger pot. These vines can be grown as houseplants.
From page 9 at this site:
WHITE BOWER VINE Ã¢â‚¬â€œPandorea jasminoides Ã¢â‚¬ËœLady DiÃ¢â‚¬â„¢
HABIT - A jasmine like climber also known as bignonia. In optional light this climber may bloom year round. Glossy dark green leaves show off the tube shaped flowers
BLOOMING - 2 inch wide funnel shaped flowers bloom the heaviest from July to September. The Pandora is available in a pink variety called Rosea, while Lady Di is white.
LOCATION - Originally from Australia Pandora prefers bright sunny locations. Pandorea is a vine and takes over quickly. To maintain an optimum size and shape staking is necessary.
WATERING - During the growth period keep evenly damp. Feed weekly until August. All-purpose soil with slow release fertilizer will prolong blooms.
OVERWINTERING - Move Pandorea indoors early, it is sensitive to the cold. Keep bright at 60 degrees and water moderately. In spring replace the top layer of the soil or repot. The plant will need to be removed from any trellis that it was staked upon and cut back the shoots.