Let \ring{K} be the integral closure of Z_p in a finite field extension K of Q_p, and let F be a one-dimensional full formal group defined over \ring{K}. We study certain finite subgroups C of F and prove a conjecture of Jonathan Lubin concerning the absolute endomorphism ring of the quotient F/C when F has height 2. We also investigate ways in which this result can be generalized to p-adic formal groups of higher height.