Solo broken?

I think this is just a terminology issue. Solo in place: solo a track and all of its routing (sends and receives). Normal solo (ignore routing): solo a track and its receives. Press the solo button: solo this track in addition to any tracks that are already soloed. The track will either solo in place or normal solo depending on the default set in preferences/audio. Right click the solo button and select exclusive solo: turn on the solo button for this track and turn off the solo button for all other tracks. In other words, solo-in-place and normal solo (ignore routing) are opposites, but exclusive solo just means "pretend I clicked off the solo button for all the other tracks." The unexpected behavior may be that normal solo (ignore routing) ignores downstream routing, but not upstream routing. Normal solo means, the signal stops here.

OK. I'm pretty confused now :). So Solo In Place is not the same as "Solo in Front"?

Yes, that's a completely different thing. Independent of all the other options, you can select options menu/solo in front. This means that solos (in either mode, in-place or normal-ignore-routing) will play "in front" of the rest of the project audio rather than "instead" of the rest of the project audio. In other words, it's like you did whatever kind of solo you wanted to, but instead of turning off all the other audio, you just turned its volume down.

Right, I'm with you now! Thanks for your patience :) With solo in front activated, is there a shortcut (modifier) for activating standard solo behaviour on a track?

Solo in front is a global option. You can assign a shortcut to toggle it via the actions window if you want, but you can't make some tracks solo in front and others solo not in front.