Makefile: macro is recast when including second file

Question

I have a make file that has two includes like this :

$ cat /src/Makefile
include ../rules.mk

Test:
    echo $(DIST_ROOT)

include src.base.mk

Test2: 
     echo $(DIST_ROOT)

. PHONY: Test Test2

$ cat /rules.mk
DIST_ROOT = $(abspath $(dir $(lastword $(MAKEFILE_LIST))))

$ cat /src/src.base.mk
srcdir = $(DIST_ROOT)/src

The issue is that the output of both is /src but it should be /.

How does this happen and how can I fix this?

Answer 1

I found the issue and a fix.
To answer my own question:
When assigning a variable with just equal sign, the variable gets cast everytime its just.
What I needed to add was ":" so it gets casted once and is set as wanted.
Based on this question.