Product Image Placeholders are not saved correctly in stores configuration section

[Perzonallica]

Preconditions (*)

1. Magento version 2.2.6
2. PHP 7.0.32
3. nginx/1.10.3
4. MySQL 5.6.37

Steps to reproduce (*)

1. Open Stores->Configuration->Catalog->Catalog page
2. Open Product Image Placeholders tab
3. Select images for placeholders
4. Save Config

Expected result (*)

1. Upload the images to the server and save the correct path in the core_config_data table which I assume is the following:

catalog/placeholder/thumbnail_placeholder
catalog/placeholder/swatch_image_placeholder
catalog/placeholder/small_image_placeholder
catalog/placeholder/image_placeholder

2. Uploaded images are visible in the Stores configuration section.

Actual result (*)

1. Doesn't matter if I upload image only for Base, Small or for every option at once, Magento always uploads the file to the server, but saves the following path to the core_config_data table:
   catalog/placeholder/placeholder
2. It seems for me that the prefix is not generated correctly.
3. So because of this it is not possible to change the default placeholder image.

Additional info

1. It works in Magento version 2.2.3 and 2.2.4

[magento-engcom-team]

Hi @Perzonallica. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

• Summary of the issue
• Information on your environment
• Steps to reproduce
• Expected and actual results

Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento-engcom-team give me $VERSION instance

where $VERSION is version tags (starting from 2.2.0+) or develop branches (for example: 2.3-develop).
For more details, please, review the Magento Contributor Assistant documentation.

@Perzonallica do you confirm that you was able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

[Shubham0492]

@Perzonallica I have checked this issue in 2.2-dev.It has been fixed.

[Perzonallica]

@Shubham-Webkul Hi! Can you please give me a link, or any info about this fix, I couldn't find it anywhere. Thanks.

[Shubham0492]

@Perzonallica Please check to 2.2-dev magento instance.This issue will not occur.

[martin-ramos]

I use Magento 2.2.6 and I have the same problem with image placeholders. I update to 2.2-dev and I have the same problem. Could you show me the code that correct this issue? or Could you tell me how did you resolve this problem?

[mropanen]

They're probably referring to this #18660