gcc -MMD omits local header files

Question

I'm invoking gcc with -MMD, and it lists some, but not all, the header files.

I've copied the FreeRTOS source into my project, include those files via #include <...>, and set the the -I path in the Makefile, and they appear in the -MMD output correctly.

But the standard #include "...." do not appear in the MMD output.

How can I solve (or debug) this?

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Updates

I'm using arm-none-eabi-gcc gcc version 10.3.1 20210621 on Ubuntu.