This is kind of an issue, not really tedious actually, but things just don't get the way I feel they should - at least unless I've done something wrong and didn't notice.
Suppose you have some sends from tracks to different busses, that may serve as different types of reverbs (typically one send per track, even more than one per bus). What you hear when you listen to a "solo" track in Ardour 0.99.3 is the sounds on that track plus their reverbs and all reverbs for every other track. What IMO you should hear is the dry signal of that track; instead, in case you activate the solo on the bus which carries the reverb for that track as well, you should hear the dry+wet signal for that track only, and not for any other track that sends signal to the bus.
This is my point of view and could be discussed (one could argue that everything on the bus should be heard whenever the bus is on "solo", in case you mean the solo as destructive); however one thing is sure, the way it works currently is incorrect because it makes no sense that sounds on the bus are heard when they're not on solo and some other track is.