What term should I use to describe situations (or bugs in software) caused by read, write, send, recv doing less work than expected?

For example, write(fd, "123456", 6); may return 3 and we need to write "456" to finish our work.

I expect any good program should do all their reads and writes in a loop until without relying that write will write everything. Am I right?

/* Implemented simple FUSE filesystem which only allows reading and writing with small buffers, very often returning that it is written less bytes that in a buffer. Some programs work, some not. Are them buggy? */