Finally, as promised, I've found some time to write this. For tupac7 and the others that have stealing file association problem with BSPlayer and can't find a solution or have decided to don't use BSPlayer for this reason:
Associations in BSP are divided in 3 groups (I don't know if it is a bug or a feature, but it seams to be a bug or BAD implemented feature).
First group is composed of extensions you can select or de-select indistinctly.
Second group's extensions are chained together. That means that if you select one of them, also the other 2nd group's extensions will be selected. The same is for third group's extensions, if you select one of them, also the other 3rd group's extensions will be selected.
FIRST GROUP
ASX
AVI
VOB
DIVX
M3U
MKV
OGM
and all custom extensions SECOND GROUP
ASF
DAT
M2V
MPEG
MPG
WMV
THIRD GROUP
MP3
MP2
OGG
WAV
Hope this could help!
--Other BSP bugs--