Options and posargs titles appear corrupted (sometimes?)

pypa/build uses this extension with `:title: python -m build` and the first title shows up correctly as `python -m build` but the following ones are `python -m positional arguments` and `python -m options` with the `build` segment lost.

See: https://pypa-build.readthedocs.io/en/stable/#python--m-build-options.