Reintroduced bug regarding spurious "variable declared but not used" warnings?

The Inform Technical Manual section 13.4(iv) ("Changes made between v6.04 and v6.05") lists among the fixed bugs:

Spurious "variable declared but not used" warnings appearing for a variable
    used only as a store destination in assembly language.

However, the behavior described as fixed can be seen when using Inform 6.34 (and 6.35). Some example code:

Constant Story "Demonstration of unexpected compiler warning";
Constant Headline   "^cf. ITM 13.4(iv)^";

Include "Parser";
Include "VerbLib";
Include "Grammar";

Class Room
    has light;

Room Start "Starting Place"
    with    description
                "An uninteresting place.";

Global read_char_result;

[ WaitForKey ;
    @read_char 1 -> read_char_result;
];

[ Initialise ;

    WaitForKey();
    location = Start;
];

Messages seen when compiling the above:

Inform 6.34 (21st May 2020)
line 17: Warning:  Global variable "read_char_result" declared but not used
Compiled with 1 warning

Inform 6.35 (in development)
line 17: Warning:  Global variable "read_char_result" declared but not used
Compiled with 1 warning

Was this bug reintroduced at some point? Or perhaps is it that the original correction in v6.05 didn’t cover this case?