This was caused by https://bugzilla.gnome.org/show_bug.cgi?id=677329,
which is fixed in Xenial (Gtk+ 3.18.9).
** Bug watch added: GNOME Bug Tracker #677329
https://bugzilla.gnome.org/show_bug.cgi?id=677329
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Bugs, which
i've notice that it happens when you hover the mouse in that terminal
with no focus, this is more like a vte issue though, so i'm reassigning
it for now. thanks.
** Package changed: gnome-terminal (Ubuntu) = vte (Ubuntu)
** Changed in: vte (Ubuntu)
Importance: Undecided = Low
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