Having the sorting field in the TCA of tt_content partly breaks the copy function in the page module
tt_content.sorting to the TCA of
tt_content (e.g. to enable the field for Extbase models) partly breaks the copy functionality in the page module. The sorting of the target position will not be calculated correctly, but the sorting of the original row will be used instead.
The only solution is to set the TCA type of the field to
none (this works for mapping it to Extbase models, but other people may have other intentions to add the sorting field to the TCA where this type might not be valid, especially if one wants to add it to the showitems). Not even the type
Discovered and tested this in version 8, but is most likely also present in 7 and 9.