Which version of "LR" are you using? Lightroom Classic (currently at version 11.5) or the cloud-centric Lightroom desktop app (current version 5.5)?
Check the sort order of the collection/album. It may be set to "Added Order" in LrC, in which case the new file from PS would indeed appear at the end. Not sure about the LR desktop app, that doesn't have an "Aded Order" sort, but maybe "Modified Date" might have the same effect.