Duplicate File / Photo Names on new Sony A77ii

[Origin]

Just wondering if anyone knows why I would be getting duplicate file names already on my Sony A77ii that only has about 5000 shots on it. This was on the same day but different SD cards when I went to copy them across for import to Lightroom. My mac was telling me (for example) DSC05150 already existed in the same folder. I know that it wasn't the same photo as I could see them both in preview.

I think I remember this happening on my A580 too, but can't remember what I did to change it and stop it happening.

Thanks

 

[Origin]

Any chance you've messed around with the File Number / Folder Name in the menu?

Just saw this. No, definitely haven't touched those settings, I went to see what they were set at and they are on the defaults and I hadn't been into that menu before.

Will see what happens next time I go out though.
thanks