The use of jump control technique provides efficient and secure ways for generating key-stream for stream ciphers. This design approach was recently implemented in some algorithms submitted to eSTREAM, the ECRYPT Stream Cipher Project. However, inappropriately chosen parameters for jumping constructions can completely undermine their security. In this paper we describe a new inherent property of jump registers that allows to construct linear relations in their output. We illustrate our results by building a key-recovery attack on the Pomaranch stream cipher. We also suggest a slight modification to the jump register configuration in Pomaranch that allows to protect against this type of attacks.