that is normal for a few types of bamboo. most notably the phyllostachys aureosulcata's will do this. usually you'll see about 15% of the culms in your grove have some sort of a distinct bend in them. be happy about it. they look great when they are all leafed out.

It is my Budha Belly that is sending up very tall zig zag culms. I have one of my Oldhamii's doing it also. Can't wait to see it leafed out.