Message bus does not respect subfolder during update process

I’m just perform an update from 1.5.0.beta8 to 1.5.0.beta9 of Discourse with enabled subfolder installation.
My Discourse was installed via official guide and subfolder enabled according to official how-to.

During update process the following picture persists:

And in the mean time in browser console logs I seen the following messages:

So seems my case is similar to this, described in this topic, but I checked and get long polling base url set:

But still update seems to pass successfully

Yep, this was a bug that @eviltrout fixed a week or so ago.