Kerbal Space Program

The contracts app is subject to a bug where it will lock up the game completely when the player opens it. This lag can be almost unnoticeable (which is what typically happens) or as much as a few minutes. The lag is directly related to the number of GameEvents.Contract.onParameterChange events have been fired since the contract app has been opened. My testing seems to imply that the scaling is not linear. Firing around 20 caused it to lag for about 10 seconds. Increasing it tenfold to 200 made it lag for over 3 minutes.

The following code run once in any contract parameter can show the issue:

for (int i = 0; i < 50; i++) {
GameEvents.Contract.onParameterChange.Fire(this.Root, this);
}

After the above gets run, if the player opens the contracts app it will lock up.

Some (not much) more details from the user that brought the issue up in the forum:
http://forum.kerbalspaceprogram.com/threads/101604?p=1665290&viewfull=1#post1665290

Also, this can be reproduced with a stock install, but not easily. Flying in and out of the flight window of a part test contract repeatedly with the ContractsApp window minimized is the easiest way to generate sufficient events for the lag to be noticeable.