In طَلْحَةٌ آخَرُ, طَلْحَةٌ has tanwīn while آخَرُ does not. This is not a contradiction: the two words have different declensional behavior.
آخَرُ is itself a diptote adjective, so it has no tanwīn even in the nominative. A word does not inherit its neighbor’s declension class.
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Restoring Declension: Indefinite Names, Al- and Iḍāfah
In طَلْحَةٌ آخَرُ, طَلْحَةٌ has tanwīn while آخَرُ does not. This is not a contradiction: the two words have different declensional behavior.
آخَرُ is itself a diptote adjective, so it has no tanwīn even in the nominative. A word does not inherit its neighbor’s declension class.