Heap region gets removed when scatter-loading

I'm playing around with scatter-loading in Keil 5.25 with armcc compiler.
Now I have a dummy project that allocates stack and heap in 'default' startup assembly file:

Stack_Size      EQU     0x00000400

                AREA    STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem       SPACE   Stack_Size
__initial_sp


; <h> Heap Configuration
;   <o>  Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>

Heap_Size       EQU     0x00000200

                AREA    HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem        SPACE   Heap_Size
__heap_limit

                PRESERVE8
                THUMB

I'm trying to use scatter file to place stack and heap at some specific memory regions. I do it like this:

LR_IROM1 0x8000000 0x4000  {    ; load region size_region
  ER_IROM1 0x8000000 0x4000  {  ; load address = execution address
    *.o (RESET, +First)
    *(InRoot$$Sections)
    .ANY (+RO)
  }

  ARM_LIB_STACK 0x20000000 {
    *(STACK)
  }

  ARM_LIB_HEAP 0x20004000 {
    *(HEAP)
  }

  RW_IRAM1 0x20006000  {
    *(+RW +ZI)
  }
}

And in main I call malloc to allocate some memory.

When I build the project, linker gives me this warning: "./dummy.sct(34): warning: L6329W: Pattern *(HEAP) only matches removed unused sections."

But I use malloc, so I should be using heap memory.
In debugger I can see that memory that I allocated by malloc was already taken by some global variable, which I presume means that heap region is indeed removed by the linker.

But why is it happening? What am I doing wrong?

I was able to force linker not to remove heap by --keep option but I still want to know what is wrong.