Bug: flat mode won't re-open emails on return to screen

Select a page in flat mode.

Open and close some mails

Select "Show Next n"
Select "Show Previous n"

The mails you opened previously won't open; nothing happens when clicking the subject

Reproduce the issue in Apache Pony Mail by selecting a page in flat mode, opening and closing messages, then using “Show Next n” and “Show Previous n.” Start by tracing the flat-mode navigation and subject-click handling. Done means previously opened messages can be opened again after returning to the page.

Written by the indexing model from the issue text.