It is not possible to break minecarts when they are moving.

Thank you for your report!
However, this issue has been closed as Cannot Reproduce.

We were unable to reproduce the problem you are describing. Carts can be broken when they are moving, if your aim is accurate. (Using a sword may help you)

Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Feedback – 📖 Game Wiki