Strange Brake Behavior

[jklaspok]

I know this is not a 987 forum, but due to the similarities and the fact this forum has some very knowledgeable Porsche people; I thought I would ask here.

I own a 2006 Boxster S where the brake booster works well except when I push in the clutch and tap the brakes as I come to a slow stop. After a few taps it becomes hard as if the booster is no longer operating. Under all other conditions the booster works as it's supposed to. Has anyone had or seen this problem? If so, how was it rectified?

Thanks