I suspect that this is a race condition between synaptic read the package cache and packagekit. Packagekit gets a org.freedesktop.PackageKit.StateHasChanged "cache-update" signal when synaptic finishes its reload operation. This is a bug that seems to be caused by improper locking.
I would welcome if you could check if you have packagekit installed when the error happens.
I suspect that this is a race condition between synaptic read the package cache and packagekit. Packagekit gets a org.freedesktop .PackageKit. StateHasChanged "cache-update" signal when synaptic finishes its reload operation. This is a bug that seems to be caused by improper locking.
I would welcome if you could check if you have packagekit installed when the error happens.