My guess is that L2.net talks a very similar way like Walker reads & shares the packs same with L2 client does. So when u load & run L2.net first, it'll temporary "fix" their communicating address between L2 client & L2W, then when aftewards load L2W, it loads as if its already verified.
Seeing so many cases that some ppl's walker still says "Not Verified" on the front page, but then after login on characters, all the functions is actually working fine, this tells me that the way Walker verifys ur subscription is only merely on the outside, once you pass the verification process, it just lets ur walker connection continue to process towards L2 server & talk to it. If u didnt pass their subscription verification, the walker server would return a signal to NOT allow ur walker continue process to L2 server. When regardless of the verification process, the walker were design to originally talk to L2 servers anyways, so now lucky Fakaman discover that using L2.net to break the gateway to open a static path for walker to talk straight to L2 client which bypassing walker server's verification, that's why u must open a client of L2.net first before run another client of L2walker. That makes lotta sense to me.
Thou this trick is pretty smart & tricky, I see few troubles here,
ppl who having slower connection would suffer from spontaenous disconnection between the L2net & L2walker, thus u'd be stalled from loading multiple instances of walker. Becuz at the same time when u trying to load L2walker, L2net is still "constantly" communicating with L2 servers. For players who used to be able to load 5 IG client with little lags, now with this trick, u might have more lags, & random DC's. CPU usage would be a bit higher. That's also why someone's not getting their 3rd or 4th client working & stuck at the "You're logging on" screen, its becuz your connection is so busy that ur pc never got back the signal u sent to L2 server & L2 server didnt return ur "Go' signal back to you, so ur 3/4th client which got stuck will forever stuck there unless u "refresh/restart" the process, which is to re-open a new path of communication until u got the signal back. Which in this case it would be pain in the ass, imagine if you trying to load a full 9 men train, u would have to reload all 9 x2 18 client one by one again. At this point is not about how fast ur PC runs or how much ram no more.
The other thing is that this might only last for this update or the next few until either walker/L2net changes their comunication ports/protocols.