forward port commit 1752405 to trunk using
svn merge -c1752405 ^/tiles/framework/branches/TILES_3_0_X .
TILES-585 – Definition cascade attributes duplicated values under high load
git-svn-id: https://svn.apache.org/repos/asf/tiles/framework/trunk@1752407 13f79535-47bb-0310-9956-ffa450edef68