When you search for files in Eclipse, multiple applicable files are displayed in a tree structure in the search window below.
Double-click each file to open it,
It will be opened to overwrite the same one tab (only one tab will always be displayed).

Before, this was not the behavior, and every time I double-clicked on a file to open it, it was opened in a new tab.
Suddenly, this was the behavior.

A bug in Eclipse?

I want to open each file in a new tab as before.
Please teach me.

Supplemental information (FW/tool version etc.)

Eclipse Platform
Version: 4.8.0.v20180611-0656