Android Unusual lines on Sony Xperia M display

[nRiTeCh]

I gifted my dad Sony Xperia M on his B'day a month ago. Phone was bought from a wel-known retail outlet with proper bill and box.

Since past 10 days, dad is complaining that when he unlocks the phone, lines appear on the display and disappear in some seconds. This doesnt happen on every unlock or daily but randomly and on random days.
Till now it has happened thrice.

He hasnt dropped the phone nor any similar incident has occurred.

Once unlocked, phone performs normally-- no hangs, reboots, call drops, no camera issues, performance or battery issues, colors too are displayed accurately etc.

What could be the problem or the reason for those lines?

 

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Looks like a faulty screen, have seen those lines appear some times in drop tests.

Question is how do you convince sony to replace it under warranty.

 

[nRiTeCh]

There's nothing to convince as I browsed through Sony official forums and many people are facing this issues and have got replacement phones or display.

Compact-Screen-Lines-and-Pixelation

My Z1 screen has colorful lines

I just want to know what causes this??
Some people say after a firmware upgrade the issue got resolved but thats just handfull of them.
And I dont want to play with its f'ware or ask dad to tinkle with that as its under 11 months warranty.

 

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Go for a replacement then, i've never heard of firmware fixing something like this. Dodgy screen batch.