How does MATLAB work when I have a structure and 'options' being set from inside and odesolver?

Suppose I have a structure k with these elements range, init and options. I noticed that since I put k inside ode45 I have an error when it calls @simp. This error is because inside k I have options. I know it because the program works well when I use options outside of k and delete k.options. So I guess it's something to do with options is being called twice or more. I forgot to mention that I called Events from inside options only.

[x,y] = ode45(@simp,k.range,k.init,k.options,k)