Welcome to 2CarPros.
Yes, that is a problem. If you used the vehicle since you did this, the system should be flushed and inspected by a trained individual. If it wasn't used and the brakes never applied after the mistake, remove everything from the master cylinder, wipe everything clean, and refill with brake fluid. I would still have it looked at for safety.
https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system
Let me know if you have other questions.
Joe
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Wednesday, July 31st, 2019 AT 6:34 AM