Good morning. I have 2 re-rooted plants on the terrace, planted last October. They are in pots of about 70x25 cm 30 cm high. in full sun from 8 am to 1 pm. They resisted winter perfectly, even if the terrace is ventilated. At the end of February I am fertilizing with a universal fertilizer (miraculous growth of saratoga) every 7 days, and the plants are full of new buds and new leaves. For some days the old leaves have suddenly dried up and almost all of them have fallen. Plants continue to bring forth new leaves, in abundance, but why have the old ones fallen? it's normal? there are no parasites, the leaves are dark green, they become brownish and fall. A nurseryman told me that it is normal foliate replacement.
in fact, if your plants are well, and have many shoots, I can confirm what the nurseryman told you; in fact it often happens to think that the leaves of evergreen plants are eternal, in fact it is not really so, because even the evergreen plants replace the leaves, only that they do it gradually, and have no periods during which the plant remains completely bare.
In particular, this fact of the trachelospermum jasminoides that suddenly loses its leaves, happens for the specimens grown in pots.
Since your plants know well, they are healthy, they are sprouting and producing new vegetation, you don't have to worry about that much; since the loss of the leaves is not causing any vegetative problems to the plant.
Generally the trachelospermum change the leaves in autumn, they become red, almost brown, and fall rapidly; the fact that your plants are doing it in the spring is perhaps due to the fact that the 2011-2012 winter was decidedly very rigid, and therefore your creepers, exposed to the cold and to the bad weather, suffered a little; but don't worry, when the spring temperatures arrive your plants will recover quickly.
However, always remember to water only when the soil is dry, avoiding water stagnation or excess watering; the fertilizer is supplied every 15-20 days, avoids the excesses, which can over time, be harmful to the plants.
If your trachelospermum is in the same pot for a long time, I suggest you to repot, in autumn, replacing all the soil with good universal soil, mixed with little sand, to increase drainage.