While in survival I was riding a waterfall down, and a simple dirt block was in the way at head level, so I went to break it after I had came to rest against it. It didn't fully break and started the breaking process over. After this happened about three times I slid into it and it reformed again, essentially suffocating me in it.

I went back to said block and tried again both with the water pushing me (same result as above) and again while standing still (normal block break).

Not a major bug but enough to inconvenience some people, especially when just trying to remove a dirt block in the way.