If ~/.local/bin was already in your PATH when env.bash is sourced, and opam's bin directory is earlier in PATH, the default dune will be the one from opam

[gridbugs]

The dev preview installs dune to ~/.local/bin, and the env.bash script checks whether ~/.local/bin is already in PATH before prepending it. I happened to already have ~/.local/bin in my PATH when env.bash was sourced, causing it to do nothing. However I also have ~/.opam/default/bin/ in my PATH at an earlier position to ~/.local/bin. This meant that after installing the dev preview the recommended way, the dune command on my computer runs the one installed with opam and not the dev preview.