Noonan in New Lager Brewing pp26 says,
"One of the consequences of forced malting is insufficient hydrolysis of beta-glucans to glucose by beta-glucanase enzymes which are denatured above 140F and do not usually survive kilning.... With reasonably well converted malt, manageable amounts of beta-glucans may be liberated from hemicellulose by proteolytic enzymes during a 95-113F (35-45C) mash rest and contribute to a beer's fermentability, body, and foam head."
Palmer in How to Brew, 3rd pp145 says,
"Most of the beta glucan in barley is degraded during malting (from 4 to 6% by weight to less than 0.5%) ... for well-modified malts."
What this seems to be saying is that for well-modified malts, beta-glucanase has been denatured and is no longer available to break down the 0.5% of remaining beta-glucans. However, by resting the mash at 95-113F the proteolytic (!?) enzymes will free up these remaining beta-glucans such that they can contribute to a beer's fermentabilty, body and head.
So, does this make sense to anyone?