I remember reading some indicators in the original TA-lib code aren't coded properly, there could be bugs or different algorithms. The other side of coin is whether MT4 indicators are coded properly... I guess it is always best to check the code yourself and test if the indicator is actually telling you the market story you are interested in.

Jurik is normally closed source but there are decompiled versions on mql5 website, google as 'Nikolay Kositsin Jurik'. However understanding the decompiled code is hard. There are some repainting implementations of Jurik indicators on mql5 website as well, obviously avoid them.