If the patch is already on, meaning the buprenorphine is already in your system, and you take your hydromorphone you wont go into precipitated withdrawal. Youd only go into precipitated withdrawal if you had hydromorphone built up in your system and then went and introduced buprenorphine into your system.
Buprenorphine out competes hydromophone in terms of their respective affinity for opioid receptors. When hydromorphone is already attacked to your opioid receptors and you flood your system with buprenorphine, the buprenorphine will essentially knock or rip all the hydromorphone off your receptors, causing you to go into violent and immeditate withdrawal. But if you already have buprenorphine attached to your receptors and ypu introduce hydromorphone to your system, with its weaker affinity for opioid receptors, it wont rip any buprenorphine of the receptors that it is already attached too, and the hydromorphone will only attach to receptors not already filled by the buprenorphine already in your system.
That is the laymans explaination.