I had already read those before I posted. But in fact I found the issue!
The problem was simply bad permissions in my NTFS volume. I followed all the guides I found online on how to set those up properly for a shared external drive and even so it didn't work. I finally decided to copy everything out of it, format and copy all back. And now it works just fine when attached to my router.
And BTW, is there a list of the supported partition types? I know about NTFS and I guess FAT32 should also be, but does it support Linux generated partitions like ext3?
Thanks!