Block deletion

When I click on a new email to delete it, sometimes a block of messages is greyed out, with the pssibility of deleting in error. What can I do to stop this?

Are the messages greyed out part of the same conversation?

For those dealing with seemingly intermittent or accidental POP3 inbox message deletions in 7.x, this may describe the issue and why it isn’t more commonly known:  when using category-based groups to organize messages, selecting and deleting (via keyboard, toolbar, or context menu) the top-most message in any group will cause the new top-most message (formerly second message in that group) to be selected along with the group heading.  Thus, pressing delete again removes the entire group and categorized messages.  Clearly, this makes line-by-line message deletions annoying when categories are in-use.  In my case, I have new messages automatically assigned to a default category via Rule, so new messages pile up under a “default” group.  When deleting these new messages from the top-down, I have to be sure to click or press the arrow key to deselect the header between each deletion.  An update to fix this auto-selection would be greatly appreciated!