I have no idea what happened or why it happened. All I know is that Episode 15 should logically have taken place before Episode 9, not sure if one was brought forward or the other was pushed back. There's probably a few other episodes which have been shifted around slightly as well. This may have been the production order rather than the intended broadcast order or, given that they are all largely stand alone episodes with no overarching story arcs, someone may not have realised the importance of the order between these two episodes.

Funny story here. When JMS was working on a spin-off series after Babylon 5, called Crusade, he wanted to make another huge scale overarching and deep storyline, but the network wanted space brutes in space with action, fights, and brawls, in space. JMS wasn't happy with this but made a few episodes like that to appease them then tried to swing it to be more like Babylon 5 in scope. In the process, the crew uniforms changed. The network got wind of this (I mean, who would even suspect that JMS would try to make another show as deep as Babylon 5 straight after finishing Babylon 5?) and cancelled what could have been an excellent series. JMS et. al. went back through the recorded episodes and decided on which way they should be ordered. So, now the official order of the episodes is not the original broadcast order, and this means that in one episode they change uniforms to the new ones, then back to the old ones, then back again! The story works better this way, as long as you ignore the uniforms...

Some fans have even created a "laundry accident" explanation.