GCC Linker unexpectedly moves location counter backwards

Question

I am developing new RTEMS BSP and I am modifying linker scripts

I modified this linker script file

    .rwbarrier : ALIGN_WITH_INPUT {
        . = ALIGN (bsp_section_rwbarrier_align);
    } > REGION_DATA AT > REGION_DATA

    .vector : ALIGN_WITH_INPUT {
        bsp_section_vector_begin = .;
        . = . + DEFINED (bsp_vector_table_in_start_section) ? 0 : bsp_vector_table_size;
        bsp_section_vector_end = .;
    } > REGION_VECTOR AT > REGION_VECTOR

Lets suppose that we need to put .vector section in the middle of some memory region thus we need symbol bsp_section_vector_begin to be aligned to 128, so I added this one line:

    .vector : ALIGN_WITH_INPUT {
        . = ALIGN(128);
        bsp_section_vector_begin = .;

Now I get this error:

[build] linkcmds.base:xxx cannot move location counter backwards (from 0000000060022380 to 0000000060022370)

Which is pointing directly to this line

. = . + DEFINED (bsp_vector_table_in_start_section) ? 0 : bsp_vector_table_size;

But when changed this line to:

. = . + bsp_vector_table_size;

There is no error, linker is satisfied and system exceptions are working.

My question is: how can such an expression like this:

. = . + DEFINED (bsp_vector_table_in_start_section) ? 0 : bsp_vector_table_size;

evaluate in a such way it try to move location counter backward? I am sure bsp_vector_table_size is positive number, and my experiment confirmed it. . = . + 0 works as well. What is wrong with this espression?