Hi there,
I’m not entirely sure what you were referring to here. Do you mean the bulk-edit dropdown option for setting sale prices as displayed here?

Link to image: https://d.pr/i/Md582C
If so, then it seems to be working fine for me on my test site. If I set it to “0”, then the sale prices are set as “0”. If I leave the field blank in the bulk-editor, then the variation sale prices are set as blank as well.
If you are seeing different behavior, then it could be caused by either a conflict with your theme or with another active plugin on your site. We address this type of problem by asking you to temporarily disable all plugins except for WooCommerce, and switch back to a default theme like Storefront.
After that, check to see if the issue is gone. If that resolves the issue, then re-enable the theme first, and then plugins one at a time until you find the one that’s causing the conflict.
You can read more about conflict testing in our Self Service Guide here:
https://docs.woocommerce.com/document/woocommerce-self-service-guide/
On the other hand, if you were referring to something different, then please send a screenshot of what you are looking at / referring to. I recommend https://snipboard.io for easily sharing screenshots – please follow the instructions on the page, then paste the URL in your reply here.
I hope that helps!
Plugin Support
Yuki K. a11n
(@yukikatayama)
Automattic Happiness Engineer
We haven’t heard back from you in a while, so I’m going to mark this as resolved – if you have any further questions, you can start a new thread.