To reproduce, run guestfish, then type:

alloc /tmp/test.img 200M
run
sfdiskM /de       <--- now hit the [TAB] key

Result:

*** glibc detected *** /home/rjones/d/libguestfs/fish/.libs/lt-guestfish: double free or corruption (fasttop): 0x000000000065df10 ***
======= Backtrace: =========
/lib64/libc.so.6[0x7ffff7431986]
/home/rjones/d/libguestfs/fish/.libs/lt-guestfish[0x413149]
/lib64/libreadline.so.6(rl_completion_matches+0x63)[0x7ffff7976c63]
/lib64/libreadline.so.6[0x7ffff7976d1a]
/lib64/libreadline.so.6(rl_complete_internal+0x123)[0x7ffff79782c3]
/lib64/libreadline.so.6(_rl_dispatch_subseq+0xd2)[0x7ffff796fd72]
/lib64/libreadline.so.6(readline_internal_char+0xa0)[0x7ffff7970530]
/lib64/libreadline.so.6(readline+0x55)[0x7ffff7970a35]
/home/rjones/d/libguestfs/fish/.libs/lt-guestfish[0x4142b4]
/home/rjones/d/libguestfs/fish/.libs/lt-guestfish[0x41514c]
/lib64/libc.so.6(__libc_start_main+0xfd)[0x7ffff73dab8d]
/home/rjones/d/libguestfs/fish/.libs/lt-guestfish[0x406a49]

Version:

git 5d78de834c53bfe29d2cc0397ac093428abe8425