My Time Capsule (4th Generation) is no longer creating that 'pop up' disconnect message.
In fact, I have not seen a disconnection [or log of disconnect reconnect] message now for a week or so.
It just seemed to have faded away, no smarts from me...
In the mean time, I have shut down and restarted my iMac several times [for other reasons]...
Although the 'nuisance' has gone, I am going to try to prompt it to return, by restarting the Time Capsule.
Incidentally, there appears to be some confusion in this discussion...
a) Version 7.6.1 is the Time Capsule [and AirPort Extreme and AirPort Express]
latest firmware. That is the one you should be using.
b) The AirPort Utility had an upgrade to Version 6.0 recently, with nice looking Graphics,
but omitted some functionality...
[DHCP Clients table, Wireless Clients table including a graph of signal strength, Logs].
Version 6.0 does provide more sensible consolidated information
on each wireless client, if you hover over the wireless client name.
c) AirPort Utility version 5.6 has one other nice feature.
You can open separate a window for each Airport Wireless Device on your network,
which I found handy when adding a new device.