Before the Samsung Galaxy Note5, previous Note models were designed to prevent you from inserting the S Pen the wrong way with the top of the Pen going into its housing first. But with the Galaxy Note5, Samsung created a spring-based method to help users eject the pen out of the phablet. And with this new technology, Samsung disabled the safety mechanism that prevented the S Pen from being inserted backwards.
The big problem for Galaxy Note5 users is that should they accidentally insert their S Pen backwards, it could permanently damage the phone. Either the S Pen gets stuck inside the device forever, or the spring release technology is damaged and can never be used again. Either way, your new pride and joy is broken, and the S Pen detection feature won't work anymore.
If you own the Samsung Galaxy Note5, let this be a warning; you need to make sure that the S Pen is replaced the right way. More importantly, you need to watch those you lend your phone to lest they replace the S Pen incorrectly. And that certainly includes your kids, who might not realize what they are doing when they try to put the S Pen back into its home.