Liquid variables with filters are not being interpreted correctly

[sparanoid]

Input:

<!-- A global capture defines elsewhere -->
{%- capture theme_base %}{{ site.theme | prepend: "/themes/" | relative_url }}{% endcapture -%}

<!-- Show the image -->
{% svg "{{ theme_base | prepend: site.assets }}/img/logo.svg" %}

Error:

Error: No such file or directory @ rb_sysopen - /path/to/jekyll-site/{{ theme_base | prepend: site.assets }}/img/logo.svg

Other filters like plus, downcase are also affected.

My workaround:

...
{%- assign logo_base = theme_base | prepend: site.assets -%}
{% svg "{{ logo_base }}/img/logo.svg" %}