Why are you doing this?

cont is being deleted there, i'm making sure it's not in m_desktopContainments anymore for not even an instant.
desktopContainmentDestroyed wasn't even called before as it's disconnecting the connection before destroying

catches also containments of other activities

No it doesn't - you're looping through m_desktopContainments.value(activity) so only things of the same activity.
Either your comment is nonsense, or your code is, or both.

yes it does.
what i mean is:
insertContainment() called with an activity that is not the current one (which will happen at startup, because insertcontainment is called for every containment, also for those in activities other than the current one), it still catches it
i can change the comment a bit, but it really does what i was meaning

i could just remove that disconnect, the thing is, i'm always hesitant to change things in ways that may have had a reason.
that disconenct was added somewhere back in 2014, i can test removing it if it still has a reason

apparently if it's managed just by the signal it seems to be too "late", as the containments don't seem to be cleaned in a single startup from the config file and i sometimes get crashes when i change activity