1. Click 'Edit description' and insert a large-sized image e.g. [[File:Chaoscope sphère.jpg|thumb|1333x1333px]]

2. The Board description will display the image in full size making Flow board unusable

3. The Board description width settings do not get applied to inserted images:

.flow-component.flow-board-page .flow-board-header 
   width: 34%;

or

.flow-board-header 
    word-break: break-word;
    max-width: 700px;

4. Flow board handles large-sized images correctly: