Dear Maintainer,

when switching to the overview (pressing super key or using the active
top left corner), a message is written to the syslog containing

g_closure_unref: assertion 'closure->ref_count > 0' failed

For every extension that is enabled this message seems to be logged too,
but even without an extension it is logged at least once, so with 4
enabled extensions it's 5 messages with every switch to the overview.
When being awakened from sleep/hibernation, this problem is worsening,
with more and more such messages appearing, also leading to severe lag
(multiple seconds). Re-login resets the problem, but it quickly
accumulates again.

There is an Ubuntu bug (2045632) without solution, pointing to enabled
extensions, but my systems shows at least one message even with all of
them disabled.

I currently have no idea how to give you further information about this,
if you have any clue, I'm happy to assist hunting that bugger down.