Adoptable Storage Question

[AndyCr15]

I've not actually used it yet, so I wonder if anyone could explain something for me. I recently changed my mothers phone from a Moto G 1st Gen to a 3rd Gen, running Marshmallow.

When I put the card in, it asked if I wanted to use it for adoptable storage, I did.

Within a month, there are low memory warnings, although the SD Card is empty?

We've cleared the cache now, which has given some breathing room, but why hasn't it just expanded into the SD card?

Then, how do you explain the maths of this?

1.7GB + 7MB does not equal 3.38GB...

Thanks for any help

 

[AndyCr15]

I've checked on XDA, someone else has the same issue, but no-one has answered there either. Is it simply a broken feature?

 

[AndyCr15]

Yep. Done that.