Yup read this article as well thanks.
I think, lets not get into a debate of why would ppl do something like that, the issue here, regardless or whether or not they put it in the manual, is an issue of Fair Use.
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Nonetheless less, to contribute on this issue.
Let me update on what happened when i brought back to service centre this morning.
Service Centre Location: 1 Commonwealth Lane #01-01
Service Date: 26th August 2015, 10:10am
Service Staff: Rowena
Passed them phone, told them it was probabaly the S-Pen issue when inserted backwards. Staff was unaware of this existing problem. Brought back to back room for servicing.
Came out 5 mins asked if i would mind a firmware reset, i told them not neccessary it should be the S-Pen Problem. She look puzzled, i said if you don't mind u pass me another of your sets i will show you.
Went back took out a Service Set, the counter staff video taped the whole thing, i took the set flipped the pen over and inserted slightly, i asked the staff to insert it herself so that she could feel that there was little to no resistance and no force required to insert it in reverse, she pushed in all the way, Pen got totally stuck, everything was on her video.
She brought the pen back to service staff behind, came out 5 mins later and confirmed that when they did managed to take the pen out the sensor was broken as well. (Funny thing is the demo set was difficult to take the pen out when inserted backwards, mine was relatively easy, probably becos i only accidently put in half way.)
Anyway they mentioned that they have no new Mobo or parts to fix yet, also when i enquired on 1 to 1 they said they don't practice at the service centre.
So they said you leave here and they try to fix and get back to me, i counter proposed that since they already broke their own set, you fix yours first

, So agreed they will, wait for parts, fix theirs, or check with management on what to do if need to do 1 to 1.
I filled in relevant forms took photo of forms and took back my phone, they will get back to me shortly.
I reiterated i do not mind waiting just do not make me pay for fixing this problem, service staff also said no worries as she has it on video herself to show how easy it is for this to happen and will discuss with the team.
Service level through out was very very good i must say. How to get mad when they let you break their own phone to prove a point .. haa haa ..
Will keep everyone updated.
And to the rest of you, don;t try experimenting also, there is totally no feedback / indentation / catch, to let you know that inserting it the wrong way is a problem.