linux-utils | Various linux utility scripts I often have to rewrite

The reason is that the package manager relies on the information provided by the kernel (via uname(2)) to decide which versions of packages (for which target architecture) should it install. Though your base image has i386 environment inside, you still run the build on x86_64 kernel, so things become a bit tricky.

When you run the container using docker run, you pass through the entrypoint linux32 - a small program which asks the kernel to pretend that it runs on i386 hardware. However, when you run docker build, the entrypoint is not used by RUNs, so yum sees that it runs on x86_64 kernel, hence the mess with platforms. You may check this answer for more detailed explanation; the issue is pretty similar.

To build your image correctly (installing only i386 packages), run yum and other architecture-sensitive commands in RUNs under linux32, e.g.: