What can cause the front wheel to lock up when going over a small bump? I was going over a bump. When the front wheel hit the bump, it suddenly stopped moving, the rear wheel lifted off the ground, and I was thrown face-first onto the road. I sustained injuries to the face, hands, chest and knees, and had to go to emergency (see edit 2 for photograph of injuries). 

I'm fine now, but I wanted to understand this so that I can be safe next time.

This happened with two different cycles, so I know it's not a defect specific to a unit or to a model. One was an e-bike, with small wheels (maybe a foot in diameter), poor or no suspension, and was going at its maximum speed of 25kph.

Since I was asked, here's a photo of my riding posture:



The brake:



And the brake lever:


(These were taken on another unit of the same model, but they're identical AFAIK.)

The other cycle has the usual-sized wheels, no suspension, and was going at 25kph or slightly slower.

In both cases:


I was going more or less straight.
The road was dry.
I never pressed either brake.
The bump was tiny, half a cm at most, and the bike can navigate much bigger bumps at full speed safely.
The road was otherwise smooth.
It was the front wheel that caught the bump.
I was thrown over the handlebars.
There was no indication of anything going wrong before I was thrown over the handlebars — no skidding, no scraping sound, no loss of balance, nothing.
The vehicle didn't have apparent damage either before or after the incident.
I wasn't carrying any loads.
I didn't have loose clothing that can get stuck somewhere.
I wasn't applying the brakes.


Is it because the bump caused the front brake to apply spontaneously? Is there anything I can do to be safe, because at this point, I'm a little concerned about using bicycles or e-bikes any more.
If you have quick-release or bolt-up front axle that is not properly tightened, then going over a bump could cause it to come out of the fork dropouts. Normally dropouts are equipped with lawyer tabs to prevent this, but they aren't 100% effective or your bike may not even have them. Once it drops out of the dropout, the fork would then no longer be supported and would drop onto the tyre brining it to an abrupt stop, likely catapulting the rider over the bars.