Occasional "failed to read page after 10 retries" with partial encrypted backup

Attached test case shows occasional database corruption errors (at least on Windows machine):

161220 23:29:51 [01] Copying .\testdatabase\t2.ibd to F:\m7\mysql-test\var\tmp\backup\testdatabase\t2.ibd
InnoDB: Read page 0 from tablespace for space 37 name testdatabase/t2 key_id 0 encryption 0 handle 568.
[01] xtrabackup: Database page corruption detected at page 1, retrying...
...
161220 23:29:52 >> log scanned up to (1770676)
[01] xtrabackup: Error: failed to read page after 10 retries. File .\testdatabase\t2.ibd seems to be corrupted.

Try running with --repeat=100
I couldn't reproduce the same without encryption enabled.

The same test on Ubuntu 16.04 occasionally results in crash below instead:

161220 23:32:42 [ERROR] mysqld got signal 11 ;
...
stack_bottom = 0x0 thread_stack 0x48400
/m7/extra/xtrabackup/xtrabackup(my_print_stacktrace+0x29)[0x55be6b13bef9]
/m7/extra/xtrabackup/xtrabackup(handle_fatal_signal+0x2f5)[0x55be6ad25d65]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x113e0)[0x7ff8b64ee3e0]
/lib/x86_64-linux-gnu/libc.so.6(re_compile_fastmap+0x17)[0x7ff8b47c3f37]
/lib/x86_64-linux-gnu/libc.so.6(regcomp+0xd2)[0x7ff8b47c46b2]
mysys/stacktrace.c:268(my_print_stacktrace)[0x55be6ab0f7ae]
xtrabackup/xtrabackup.cc:3418(xb_register_regex(char const*))[0x55be6ab0e816]
xtrabackup/xtrabackup.cc:3508(xb_filters_init())[0x55be6ab0f224]
xtrabackup/xtrabackup.cc:3860(xtrabackup_backup_func())[0x55be6ab137be]
xtrabackup/xtrabackup.cc:7187(main)[0x55be6aafabe3]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7ff8b46fd830]
/m7/extra/xtrabackup/xtrabackup(_start+0x29)[0x55be6ab0e149]