If you have more videos in a folder which form part of a sequence, like e.g. "moviefile_CD1.avi", "moviefile_CD2.avi", "moviefile_CD3.avi", "moviefile_CD4.avi" (etc), BS.Player will indeed automatically add any
subsequent file(s) to the playlist if only one file is selected. I emphasized 'subsequent', because if you e.g. pick the CD2-file, it will only add the CD3- and CD4-files (but not the CD1-file). And if you pick the CD3-file it will only add the CD4-file. This IMHO is a very good feature, which saves you the trouble to select more files of a sequence.
I meanwhile tested and it appears that if one selects two files
which apparently belong together and form a sequence (with no further files following in that sequence) BS.Player will place both files in the playlist AND will it will still add any sequential file(s) as indicated above. So if you selected CD1 and CD2 files, in total
three (and not two as mentioned by you) files are placed in the playlist.
Further .....
..... if you use CD1-file to drag-and-drop BS.Player will start playing with the CD1 file, followed by the (auto added) CD2 file and then followed by the (manually added) CD2-file.
..... if you use CD2-file to drag-and-drop BS.Player will start playing with the CD2 file, followed by (the manually selected) CD1 file and then followed by the (auto added) CD2-file.
(
In fact, in an example where there are 4 sequential files and you would select all four of them (in stead of simply only the first) and then use the first file to drag-and-drop,the result in BS.Player's playlist will be:
CD1-CD2-CD3-CD4-CD2-CD3-CD4-CD3-CD4-CD4)
I think that sufficiently explains the how or why.
So, I would suggest to make life easy and not unneccessarily select more files which form part of a sequence, which task BS.Player is already taking from you. Or post a feature request to have an option to switch off the auto-adding of sequential files by BS.Player.