Probably not an equivalent problem on recumbents, but ...
A few weeks ago a buddy (a physician) told me about a serious injury he received when clipping into his Speedplays on his DF. The cleat didn't completely clip in, he pushed down hard on the pedal to get started. Instead, his foot slipped off the pedal, he literally catapulted over (to his left), landed hard on his head and his left shoulder. He was knocked unconscious for more than 20 minutes. Given that this was a concussion he suffered proximate memory loss and serious shoulder injury (but, fortunately, no broken or separated bone). Wisely, his own physician recommended against open road cycling for several weeks to be certain that there wouldn't be sudden dizziness or disorientation.
Yesterday, I was starting out on a training ride with a few buddies and the exact same event happened. Fortunately there was no loss of consciousness. BUT my buddy's helmet was cracked in half. Imagine if he hadn't worn that helmet.
My own issue has more to do with the SIDI shoes I wear ... when I wear them. (Another reason I wear sandals or shoes with recessed cleats). The `plastic' bottom of the SIDI shoes slips on the pedal when I try to clip in. In very hilly terrain, when starting uphill trying to clip in ... I have to be very, very careful not to slip off the pedal with the shoe. If I `miss it' I usually tear some skin on the ankle and have to scramble fast to recover my balance on the bent.