10.3 Clarification on assigning unsigned literal to signed

[michael.metivier]

A non-negative integer constant expression of essentially signed type may be assigned to an object of essentially unsigned type if its value can be represented in that type.

While Rule 10.3 has this Exception for constructions similar to

Code:

uint8_t u8a = 0;    /* By exception */

there does not seem to be a similar exception for the inverse

Code:

int8_t s8a = 1u;    /* Compliant? */

Our current analysis tool flags this as an error, but this assignment seems no more dangerous than the one given by the Example. Is there a specific rationale for why this assignment should not be allowed, given the condition of the Exception

if its value can be represented in that type.

?