Setting a layout variable into channel form {custom_fields} loop doesn't work

[pixiwooh]

Description of the problem
Issue tested on 2 different installations.

In a channel form, I try to store each {field_name} into a {layout:set:append} variable list so I can loop through this list into the wrapper layout template and dynamically show some stuff based on the fields name.

`{exp:channel:form channel="mychannel" entry_id="{segment_3}"}

{custom_fields}
{layout:set:append name='lv_the_fields_name'}{field_name}{/layout:set:append}
{/custom_fields}

{/exp:channel:form}`

The {layout:set:append name='lv_the_fields_name'}{field_name}{/layout:set:append} is not being parsed. For each custom field of the loop I got {layout:set:append name='lv_the_fields_name'}my_field_name_well_parsed{/layout:set:append}

My end goal is to show into the wrapper layout a sliding help panel for each custom field, like this :
{layout:lv_the_fields_name} {embed="modify/_help_panel_{value}"} {/layout:lv_the_fields_name}

But since the custom field's names are not append to the layout variable array, I can't.

How To Reproduce
Steps to reproduce the behavior:

1. Create a channel form
2. Loop through the fields with {custom_fields} tag.
3. Try to show the the names of the custom fields with {field_name} to be sure it works.
4. Create a dynamic list layout variable between the {custom_fields} tags with {layout:set:append} tag pair to store every field name
5. You should see the layout:set:append tags not parsed (but the fields names well parsed) in the front-end
6. In the wrapper layout used : impossible to show the values of the dynamic list layout variable.

Error Messages
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Environment Details:

• Version: 5.2.2
• PHP Version 7.1.18
• MySQL Version 5.0.12-dev
• OS: Windows
• Web Server: Apache

[pixiwooh]

Is there anyone to look at this please?

This is a show stopper for me.