This probably isn’t what happened to you, but just a word of advice: careful with CSS PIE. I have used it in sites in the past and it has had the tendency to cause elements on the page to behave strangely.
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As @theacefes says PIE can be somewhat troublesome. I always recommend using it only on the essentials as it does have problems with shadows, especially in responsive design.
I’d recommend using it in moderation only on bits that look broken or absolutely require gradients/radiuses. Shadows ultimately are more visual flair, if you can get away without using them make sure you do.
Keep in mind also that if you do use shadows with PIE make sure to set the background colour of the element because it will otherwise show the shadow underneath the content of the box.