NetTools uses local caching to improve the performance when viewing the permissions in ACL Browser and GPO Explorer.  The cache is used to cache Control Assess Rights GUIDs and resolved SIDs, this makes viewing the permissions of subsequent objects significantly faster.  ACL Browsers and GPO Explorer use the same cache to improve performance across these options.  If ACL Browser and GPO Explorer interrogate the same forest then both options will benefit from the caching.  However, when they are pointing at different forests, the cache is cleared and caching is started again when a different context is detected, resulting in an initial performance hit as the cache is reseeded.