On my phone, I went to upload an image to a card. In the photo browser, there is an option to resize the image prior to uploading (you can choose L, M, S). If you choose any of those options, rather than the actual image size, then the resulting image uploaded is rotated sideways.
I see the same behavior when doing a similar thing on Are.na’s web interface.
It seems like maybe there is a discrepancy with how the EXIF is being interpreted or read. Some quick searches turned up:
Not a priority at all for me, just wanted to report