After some analysis I found that our application sets as default HTTP request creator the ClientHttp one, instead of the default BrowserHttp. Doing this seems to somehow have side effects on the normal operations of Lightstreamer's API.

For the time being, I have worked that around by forcing the usage of BrowserHttp creator for requests created to the Lightstreamer URL, and now the browser process shuts cleanly down when its window is closed.

Thank you,
Emilio

PS
As a side note, I observed that I was not able to establish a streaming connection when using ClientHttp creator. I can now do that using BrowserHttp.