Something went wrong with this change, @lubos. Now, if a form is copied to another, content of a custom field (which may have been modified from any default when the source form was created) overwrites the existing default content for the target form under Form Defaults.
For example, a Notes custom field is created on both sales quotes and sales invoices, and the sales invoice custom field has default content set:
A sales quote is created with the following content in its Notes field:
The sales quote is copied to a new sales invoice. At that point, the content of the Notes field from the sales quote carries over to the sales invoice. This seems appropriate, because information related to the specific sale should carry forward. However, this seems to contradict what you wrote about the change at version 18.7.31. @sharpdrivetek complained that default content for the target forms were not used, and you said that had been fixed, implying that default content would be substituted for specific content. If that is what you meant, it is not happening.
More importantly, I don’t think it should happen. Previously, the Copy to function has overridden defaults with transaction-specific information. In my opinion, that is as it should be. Otherwise, what is the point of having matching custom field labels?
The bigger problem, however, is that the Copy to action actually changes the Form Defaults for the target form. After the foregoing action is complete, the default custom field content for sales invoices has been changed to match the content of the custom field from the sales quote. What was specific content for one transaction form has become default content for a different type form.
I am putting this topic into the Bugs category.