I have recently updated from v3 to v4 of dhtmlx.
I had an issue a while ago here concerning ie8 performance: viewtopic.php?f=17&t=27134&start=0&hilit=performance
For v4 it seems like its back for me, however doWithItem() is the culprit. See here: i.imgur.com/lWL7uKm.png
If so is there an updated version for v4 that addresses this issue?