Has this camera passed the 10k mark yet? If yes the camera will numbering system may revert or change?
This happens (by industry convention) for as long as a camera is set to save its JPGs under the AdobeRGB colourspace, rather than the more usual sRGB.
The first character is replaced with an underscore (by the camera).
The same naming convention is used for Raw photos, while the camera's set this way - even though that setting makes no practical difference to the Raw file itself.
Check the cameras file naming.
Also did you make any changes in the cameras menus recently? Specifically the color space. If I change the color space on my cameras from sRGB to ARGB it changes the file naming to add an underscore at the front of the file name.
Richard, that is what is happening. I read an article recently that made me decide to switch to AdobeRGB color space rather than sRGB. I just tried 2 shots. One in AdobeRGB and the other in sRGB and then looked at the files in Finder. The AdobeRGB file was _BM_xxxx while the sRGB file was KBM_xxxx. Thanks for explaining it.