It's not a new behaviour. It's the Transfer to Temporary Filename feature.
See https://winscp.net/eng/docs/resume#automatic and
https://winscp.net/eng/docs/ui_pref_resume

since a few winscp versions i noticed that if i edit a file with "f4" with my local editor and the file gets re-uploaded and saved it is not saved with the original ownership and permission but it is changed to the current user (in this case root) with 0700 permission. this behavior is new to me (don't know with which version it was introduced) and is a really annoying bug for me.

upload options for "text"
- set permissions: not checked
- preserve timestamp: checked
- filemask empty

is there a new/old setting where i can preserve the current permissions and owner or is this a new bug?