Masking the Catch

[rwest]

The past two years this question has been on the ASA Exam:
(paraphrased)

A foul ball is heading toward fair territory prior to first base. An infielder throws his glove at it preventing the ball from becoming fair.

If I remember correctly, the correct answer was its a foul ball. Am I the only one that thinks the defense should be penalized for this? I know the detached equipment rule is for a fair ball, but why not for a foul ball if the defense gains an advantage?