yea mine do it too and they flatten in time, it could be the tap water or perhaps just the quick growth of the leaf makes it look a lil funny while it growing.
be interestng to know why this is actually happening tho. if its retarded roots, you might see a change adding in some phosphorus, and micro nutes.
also, the pics seems a lil light on the green side, i wouldn't hesitate upping the N a bit. might just be the lighting tho