I recorded a bass line and a lead vocal line.  I added sends for the vocal to a reverb and a delay.  The bass line as some effects in the track Fx bin, but NO sends.  So, when I solo the bass line, I hear the reverb buss with the vocal along with it.  I checked ins and outs but can't understand why I here the buss.  It goes away when I mute the buss, but why does it show up in the first place?

Mutes for tracks and busses are not inclusive. Meaning, if you soloed your track and wanted all busses to be muted then you would not hear anything because, if you use a main bus, the main bus would be muted.
 
Also, if the sends are pre-fader then they go to the busses even though the individual track is muted. There is a routing diagram in the X2 users manual that shows how all the routing is done. I am not at my computer right now so can't verify the details of this but the general idea is as I have stated above.

There are options for the solo in the preference menu. Make sure they are set to meet your workflow needs.
 
CJ