{%vm%} vertical merge not working as expected

[chrisu-mi]

Describe the bug

The {%vm%} tag is not working as expected.

I import data from a Yaml file:
from ruamel.yaml import YAML
yaml=YAML(typ='safe')
with open(path_DuT_list, "r") as f:
yaml_DuT_list = yaml.load(f)

from this file:
DuT_list.yaml.txt

I use the tag in simple table.

The result looks like that, all rows are merged, even though there are actually different values:

I have a nested table looking like that

There is nothing happening, see:

I already tried to change the data type from int to string, but results are the same

To Reproduce

see code examples above

Expected behavior

First table should look like this:

Second table expectation:

Additional context

I tried the following docxtpl version: 0.18.0; 0.17.0 and 0.16.8
and also various older python-docx and jinja2 packages.