I was given a small (very smalll) rooted cutting of a kaffir lime in a pot earlier this year. It's lived happily on my east facing kitchen windowsill all summer, being watered only with soft rainwater and fed twice with specialised citrus feed. It grew another little shoot and looked happy although still only about 5" tall. Then about a fortnight ago it started dropping leaves and now it's just a bare stem.
I've been careful not to let it dry out, and also careful not to soak it or leave it soggy.
What's going wrong?