autocomplete - Very slow completion and code highlighting in Qt Creator -

i have qt creator 4.1.0 ubuntu 16.04. , have problems completion , code highlighting. need wait 3-4 secs(or more) completion code , highlight key words. wrong? qt creator 3.6.0 working normally.

i can confirm observe same problem on windows 7 after upgrading 3.6 4.1. used able tab complete function signatures , no longer works annoying. haven't tried 4.2rc yet see if fixed i'll update post once do.