Also, I wonder how many obscure bugs were introduced by using more aggressive compiler flags? The image has "lto" in the name, and at https://github.com/docker-library/python/issues/160 I see this comment:

In the future the Python developers may decide to turn on further optimizations based on this argument, for example link-time optimizations (LTO), though they haven't worked out all the bugs for that one yet.

(Thanks mastax for finding the issue!)