Here is the illustrative example:

fn foo() {
    { bar('}'); }
    { bar(']'); }
    { bar(')'); }
}

The characters within ' characters above are incorrectly treated by src/etc/rust-mode.el as closing the opening paren of the invocation of bar. This confuses Emacs in a number of ways (e.g. obviously paren matching; but also the auto-indentation gets confused too, which is more annoying).