free(): double free detected in tcache 2

After upgrading to dar 2.6.8 I seem to have hit a (different) bug. My
daily backup now fails with:

free(): double free detected in tcache 2

So far it has only tried once, and has hit that error. However, I have
never seen it before, and this is the first backup since I upgraded from
dar 2.6.6 yesterday.

I will try to reproduce it, but are there any additional options you
suggest I turn on to get any more information about the problem
(assuming it recurs)?

Here is the actual log from last night's DAR_automatic_backup.sh run
(note: I have removed a LONG list of -P options to protect the
filesystem information as I am posting this to a public list)...

############
DARsystem: ### Wed, 26 Feb 2020 02:20:02 +0000 ###
DARsystem: Current backup information (Size in 1024 bytes blocks.):
DARsystem: ..DARsystemFull: 36509724.
DARsystem: ..DARsystemDiff: 3198896:
DARsystem: ....DARsystemDiff01: 3198896.
############
DARsystem: Preparing to Create DARsystemDiff02.
############
DARsystem: creating DARsystemDiff02. Please wait.
###
No terminal found for user interaction. All questions will be assumed a
negative answer (less destructive choice), which most of the time will
abort the program.
free(): double free detected in tcache 2
sh: line 1: 108460 Aborted                 dar -s 1450M -c
/backup/DAR/novatech/DARsystemDiff02 -A
/backup/DAR/novatech/DARsystemDiff01 -R / --compression=bzip2:9 -m 0 -D
-N --retry-on-change 20 --alter=secu -P "backup" <LOTS OF OTHER -P
OPTIONS REMOVED> -X ".xsession-errors" -X "stderrdae.txt" -X
"stdoutdae.txt" -X "client_state.xml" -X "stderrgui.txt" -X "stderr.txt"
-X "xaakg.out" -X "tmp2" -Z "*.dar" -Z "*.crypt" -Z "*.arj" -Z "*.bz2"
-Z "*.bz" -Z "*.Z" -Z "*.tgz" -Z "*.taz" -Z "*.cpio" -Z "*.deb" -Z
"*.gtar" -Z "*.gz" -Z "*.lzh" -Z "*.lhz" -Z "*.rar" -Z "*.rpm" -Z
"*.shar" -Z "*.sv4cpi" -Z "*.sv4crc" -Z "*.tar" -Z "*.ustar" -Z "*.zoo"
-Z "*.zip" -Z "*.jar" -Z "*.jpg" -Z "*.gif" -Z "*.mpg" -Z "*.mpeg" -Z
"*.avi" -Z "*.ram" -Z "*.rm" -Z "*.mp3"
DARsystem: Sorry. 'dar' failed with exit code 134. DARsystemDiff02
backup aborted.
############