In a multi site webapp setup, switching channels in the channel mngr does not always work

Reproduction:

1) Start up testsuite
2) Go to channel mgr
3) open 'My Hippo Project'
4) Go to channel mngr overview
5) Open 'English Demo Site'

Now you see some _rp calls for the English demo site, but then, the 'My Hippo Project' stays active and more _rp calls are done for the 'My Hippo Project' channel.

Note that if between step (4) and (5) you first go to the 'French Demo site', it seems to work correctly