Word for phrase Good for you, bad for us

There is a phrase I have heard quite a bit recently dealing with people that are leaving the department for promotions, etc. When a person leaves, it is good for them, but bad for us.

It is good for them because they will be pursuing a new opportunity, but not so good for the department since they will have to be replaced, and others will have to pick up the slack until someone else can be hired and get up to speed.

Is there a word that means that a deal is good for one party, but not necessarily the other?

You might also consider "a mixed blessing".

A Zero-sum game, quoting wikipedia, is according to game theory:

a mathematical representation of a situation in which each participant's gain (or loss) of utility is exactly balanced by the losses (or gains) of the utility of the other participant(s). If the total gains of the participants are added up and the total losses are subtracted, they will sum to zero.

This leads on to concept of social traps (aging quoting wikipedia) ...

In psychology, a social trap is a situation in which a group of people act to obtain short-term individual gains, which in the long run leads to a loss for the group as a whole. Examples of social traps include overfishing, [...] and the destruction of the rainforest by logging interests and agriculture.

EDIT : I just realized this partly duplicates @al-maki's answer, but I'll leave mine as the quotes may be helpful.