When you mouse over a text block anchor (The little six dots handle) it says "Drag to move, click for menu). If you drag this over another article in the article list on the left hand side, you get a blue marker indicating that the text block should be able to be moved either out as a new article, or into another article. However, if you keep the mouse there, button down, you will see it "flicker" to a "not possible" type icon (red circle with slash) every now and then.

Now, if you actually let go of the mouse button, weird stuff wil happen. Another article from the list will be dragged instead, and have its order moved or be moved in as a sub-article of another.

Suggested fix: If dragging a text block to the left hand list is NOT supposed to be possible, you should get a clear "forbidden" mouse cursor, and nothing should happen on button release.