Both issues are WPML related. Polylang uses the WPML API, and therefor has the same issue.
What happens is that once a multilingual plugin like WPML / Polylang is detected, it uses the WPML API to get the label text, and not the normal WPSL labels.
When you add an English language to Polylang ( assuming your site is in English ), then you can change the label text there. If you use WPML, then you have to use the string translations to change them.
I’m aware this is not optimal, and I clearly should have shown a notifications to tell users when a plugin like WPML / Polylang is active, that you need to use the string translation to change the labels, and not the label fields on the plugin settings page.
I will make this more clearer in the 2.1 update, and see if I can make it work so that you can change the labels on the settings page, and when WPML is active, they also end up in the WPML database.