Ansible does know that if logging in as foo and sudo'ing to foo, it's smart enough to avoid doing the sudo at all.
This has been a point of contention with one user's SELinux environment where logging in as root didn't get full privs until sudoing, at which point it was proposed a setting to control this behavior.
That all being said, I'm not sure this is what you were seeing, but it can explain scenarios when ansible ignores a sudo statement.
Otherwise, sudo: True is functional, and we'd need to see more detail.