Documents panel causes last tab to be activated/switched to

[jefferyto]

 * Xed version - 3.6.6
 * Distribution - Mint 22

Issue

Drag-and-dropping a tab after clicking on a document in the documents panel causes the last tab to be activated/switched to.

Steps to reproduce

1. Open 5 or more documents (new documents are fine)
2. Show the Side Pane and select the documents panel
3. Click on one of the documents in the documents panel
4. Drag and drop one of the (notebook) tabs in the main area left or right (to reorder the tabs)

Expected behaviour

The drag-and-dropped tab remains focused/active.

Actual behaviour

The last tab in the window becomes focused/active. I believe each tab between the current tab and the last tab are focused in turn until the last tab in the window, but I haven't confirmed this.

Other information

This occurs in older versions of xed as well; the earliest version I tested was 1.4.4 on Mint 18.2. This also occurs in Pluma (mate-desktop/pluma#702).