I don't know, but since a few versions, InDesign line breaking engine is completely broken and regularly produces situations like this:
Balance ragged lines and
Keep options are off.
There is enough space down there. All lines are set to stick to baselines. I would need to drag the green text frame towards the bottom until the next paragraph can jump in to get the one word in.
Sure does look like a keep option. Check that paragraph for keep with next, and the following one for keep with previous.
Ok so I have double checked and can now give feedback on what has made me and my colleague not understand the interface correctly.
Our assumption was that the selected setting here does NOT have an influence unless Keep with Previous is checked. Just like the box Keep Lines Together. Adding a little bit of space between the different settings would certainly help to distinguish them as I have literally run into a usability problem here.
Thanks for the help!