Samsung's (NASDAQOTH:SSNLF) latest flagship phone, the Galaxy Note 5, suffers from a major design flaw: improperly inserting the S Pen can permanently damage the expensive phablet.

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Samsung's Galaxy Note 5 with S Pen. Image: Samsung

Samsung's chief rival, Apple (NASDAQ:AAPL), has suffered from similar issues in the past. But regardless of whatever flaws they may possess, iPhone sales have continued to surge. Samsung could emerge from the situation similarly unscathed, but it's an unfortunate occurrence during a time when the company's handset business has been under pressure.

Watch where you stick that S Pen
Since the debut of the original Galaxy Note, Samsung's flagship phablets have sported a stylus -- the S Pen. While reviewers often focused on the phones' massive displays, their trademark feature has actually been the S Pen. Every Samsung phone or tablet that bears the Note branding includes the stylus -- not every large Samsung phone is called a Note.

Like its predecessors, the Galaxy Note 5 includes the S Pen, but Samsung has made a number of improvements to the handset, particularly when it comes to design. Prior Notes were made out of plastic and fake leather -- the Note 5 is made entirely of metal and glass.

That redesign extends to the S Pen itself. In the past, S Pens were slightly misshapen, with one end bulging out. This bulge allowed Note owners to remove the S Pen -- a properly inserted fingernail could provide enough leverage to slide it out. The Note 5's S Pen, however, is different: In terms of its shape, it's almost completely symmetrical.

Rather than pull the S Pen out, Note owners must push it in to trigger an automatic eject feature. It's an interesting design decision, and one that might be seen as superior if it wasn't for a potentially catastrophic flaw. Prior S Pens, with their bulging ends, were incapable of being inserted backwards. Unfortunately, the same can't be said for the Note 5's S Pen.

Accidentally inserting the end of the S Pen into the Note 5 can damage the phone significantly -- and there's no easy way to fix it. It won't malfunction completely, but the sensor Samsung includes to monitor the status of the S Pen can break. If it does, the Note 5 will be unable to tell if the S Pen is inserted, and certain S Pen features will cease to function.

Samsung has addressed the issue, though not in a particularly favorable way. "We highly recommend our Galaxy Note 5 users follow the instructions in the user guide," Samsung told The Verge.

Antenngate and Bendgate didn't stop iPhone
Apple has suffered from similar issues in the past, though to its credit, took much more consumer-friendly stances.

Dubbed "antennagate," the iPhone 4 suffered from an apparent design flaw that would lead to dropped calls when the phone was held in a particular fashion without a case. Apple addressed the problem directly, and though it tried to downplay the issue, it offered a free bumper case to any iPhone 4 owner that wanted one. 

More recently, "bendgate" has plagued Apple's current flagship, iPhone 6 Plus. The phone, with its thin aluminum casing, can bend when placed under only modest stress. Like antennagate, Apple has downplayed the issue, but has since taken to replacing bent iPhones free of charge. Reports suggest that Apple plans to deliver a slightly thicker iPhone later this month.

Neither controversy had any effect on Apple's smartphone business. iPhone sales continued to rise in 2010, despite the negative publicity. This year, Apple has generated record iPhone sales as demand for iPhone 6 and iPhone 6 Plus remains strong.

The same could hold true for Samsung's Galaxy Note 5. There's little competition for stylus-equipped smartphones -- those that want one may decide the issue is worth overlooking.

Competition in the broader smartphone market, however, has been intensifying -- much to the dismay of Samsung's mobile business. Samsung's sales and its mobile profits have tumbled in recent quarters, as competition from Apple and low-cost Chinese competitors take a toll on its market share.

If that trend continues, it would be hard to pin it on this one particular design flaw. Still, it's certainly not a positive development.

Sam Mattera has no position in any stocks mentioned. The Motley Fool owns and recommends Apple. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.