E-book Editor and tabs eating up all the space

Before, when you would edit a book and opened a lot of tabs, the tabs would scroll leaving room for both the file list and the preview window. Now as tabs open, it pushes the two outer panes to the extremes so that they become unusable. Is this a bug or a setting that can be turned off?

See the included image.

This is on MacOS 26 on an M4 Pro.

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