I noticed this when I watched a HD-version of ESB. In one of the scenes when Leia, R2, C3PO, Chewie and Lando is racing back to the Falcon - being chased by stormtroopers.
When they reach the landing platform, Leia turns around, shoots and hits one trooper. When watching the trooper gets hit in slow-mo, one can actually see that they've used white PVC-textile-material (pretty much like the PVC-textile material commonly used in the advertisement industry) to replace the shin-armor..so no shin armor when the stuntman gets hit, and only the PVC-material warping up kinda like textile.