a glitch in Medic and Collector

[Soldier . . .]

so they "attack" during a medic is reviving.

Do all medic players complain about this?
Because you have a high ping and the server makes the decisions in what zombies do.
In other words you have a relative big time difference between what the server sees and what you see on your screen.

So while on your screen you just started reviving, the server sees you still walking towards a downed player.
And let the zombies still targeting you. Until the server sees that you are reviving.

Don't know or this can be solved with a server side only adjustment.