Reproduce:
Use test.zul and TestVM.java attached, it is very slow when page loading.

Cause:
syncWidth of Combobox (with inplace="true") costs lots of time in Listbox.

Workaround:
Override syncWidth to reduce loading time, see test.zul in workaround.zip attached.

Edit:

Previous workaround still a bit slow and may cause some side effects, update to fix for this case only.
Please refer to test.zul in workaround_20140325.zip attached.