Mine does it too, only between 0 - 15 brightness.
Other users have also reported this. One user said that he sent his G2 Mini for repair and the replecement screen did the same thing.
Sent from my D620R [Stock 4.4.2]
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Samsung Galaxy 5 Europa (GT-I5500) [CM11] --Rooted--
Samsung Vodafone 360 H1 (GT-I8320) [CM7.2] --Rooted--
LG G2 Mini (LG-D620r) [Stock 4.4.2] --Not Rooted--
w/ Xposed installed, for more info click here
Translated Apps (to Greek):
[Xposed] App Settings