I have been able to reproduce this problem and you're right: this seems to be a bug.
There is a way to avoid it though and that is by working with playlist.
If you put your files in (or add them to) the playlist and press the [>|]-button on your control panel (depends on skin used), the next movie should load and play with its own subtitles.
(You might want to
define the enqueue-option in addition to the default load option to facilitate easy adding files to the playlist; Note (1) I use this myself for version .86 but I did not test it for version 1.0 of BSPlayer (2) also note the name of the executable of version 1.0 is bsplay.exe and not bplay.exe like in version 0.86)