Suddenly, no brake pressure. Why?

Yesterday I had a bit of a surprise. While going backwards when turning my bike I used my front brake. It had no pressure at all and went all the way in. Felt like it had no fluid in it at all! It pumped right back up and worked fine again, but I'm not going anywhere for now.

I have no idea how this could happen. It didn't leak fluid, it isn't low on fluid either and it wasn't until braking backwards it happened.

The moving parts are brand new except inside the calibre. Was holding out on it until the bike was going in winter hibernation in a month where I'll service it anyways, but it seems it will go in early.

Any ideas?

How long ago were the new parts installed ? ..sounds like you have air in the lines, & need to be Bled
Pete

Your master cylinder has an internal leak.

I don't get how with new parts. Unless something is wrong with them (unlikely) or I made a mistake (more likely). I can't remember any parts that could possibly be put in wrong though. Maybe the rubber part on the piston..

Wouldn't something like a leak also happen when applying a lot of pressure? Because I have tested the breaks extensively and bled them by the book, ran with it for a month too.

I guess what I'm really saying is that I hope it isn't wear on the master cylinder causing it.