Panels strings are lost on string refresh

How to reproduce:
With current dev (1.14+6) i can reliably:
* Deploy and revert my translations using features_translations
* (Check translations are displayed in the UI and on the translation page)
* Refresh strings on admin/config/regional/translate/i18n_string, with "Clean up left over strings" selected
* (Note: string refresh tells us that some "left over" strings are deleted)

Then some strings are lost (consistently in the UI / on the translation page / on the translation feature diff).
The deleted strings are from text group "panels", at least some "override_title_text".