As it comes out, the Plain View mode has some issues. I have already described it in detail on the forum of Mp3tag [
https://community.mp3tag.de/t/cannot-dr ... der/41567/], but it comes down to this: some third party software [like Mp3tag or Media Player Classic] will not allow you to drop more than one file selected in Plain View mode- if those files happen to reside in some sub-folder [while files stored in parent folder that were selected & dragged & dropped via Plain View do not impose such limitation]
And to quote the developer of Mp3tag:
Getting data via
FORMATETC etc = {CF_HDROP, nullptr, DVASPECT_CONTENT, -1, TYMED_HGLOBAL};
works while
FORMATETC etc = {CF_HDROP, nullptr, DVASPECT_CONTENT, -1, TYMED_HGLOBAL | TYMED_MFPICT};
doesn't. Seems to be overly restrictive, but no problem to workaround.