Thank you for your report, the detailed description and the screens. With the help of all that, I am able to reliably reproduce this bug. Apparently the status is not shown correctly, if the package is not available (any more) in the Debian distribution. That is at least, what the missing Debian icon in your synaptics screenshot suggests. I was able to reproduce this for the package "tasque" on my machine, which is only in oldstable. This will give me leverage to find a solution for this problem, though it might be some time until I find the time to tackle this issue.
Kind regards Benjamin
