Apt Question

[Michael Milliman <michael.e.milliman@gmail.com>]

I have, for various reasons, the repositories from stable (Jessie),
stretch, and sid in my sources.list file. I have Stretch installed and
have it running for some time.  On occasion, there is a bug in Stretch
and I revert to the stable version of the package until the bug gets
worked out.  I also, on occasion, use a more advanced version of the
package and get it from sid (with a careful look at the proposed changes
to the system when doing so).  I have set synaptic to prefer the Stretch
distribution.  However, when I reload, and tell synaptic to mark all
upgrades, it marks upgrades which it will pull from sid.  Is there a way
to tell synaptic to ignore those upgrades, while allowing me to manually
install them should I wish to do so?  I had thought that telling
synaptic to prefer the Stretch distribution would have handled that, but
I guess not.  I figure I'm just missing something.
-- 
73's,
WB5VQX -- The Very Quick X-ray