Backintime seem to process taking a snapshot, but stops at final step(s).

Starting situation:
zypper dup Leap from 15.2 to 15.3.
After reboot, performed a zypper ref && zypper up, all pkgs current now.
Made an initial Clonezilla image, to be sure.


Reproducible:
Wanted to make a first backintime snapshot, does NOT work
Error on command line is:

INFO: Remove leftover 'new_snapshot' folder from last run
QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
INFO: Call rsync to take the snapshot
Traceback (most recent call last):
  File "/usr/share/backintime/common/backintime.py", line 1165, in <module>
    startApp()
  File "/usr/share/backintime/common/backintime.py", line 517, in startApp
    args.func(args)
  File "/usr/share/backintime/common/backintime.py", line 739, in backup
    ret = takeSnapshot(cfg, force)
  File "/usr/share/backintime/common/backintime.py", line 94, in takeSnapshot
    ret = snapshots.Snapshots(cfg).backup(force)
  File "/usr/share/backintime/common/snapshots.py", line 692, in backup
    ret_val, ret_error = self.takeSnapshot(sid, now, include_folders)
  File "/usr/share/backintime/common/snapshots.py", line 1036, in takeSnapshot
    proc.run()
  File "/usr/share/backintime/common/tools.py", line 1981, in run
    self.callback(line, self.user_data)
  File "/usr/share/backintime/common/snapshots.py", line 809, in rsyncCallback
    self.snapshotLog.append('[C] ' + line[12:], 2)
  File "/usr/share/backintime/common/snapshotlog.py", line 195, in append
    self.logFile.write(msg + '\n')
  File "/usr/share/backintime/common/tools.py", line 1513, in handler
    self.callback()
  File "/usr/share/backintime/common/snapshotlog.py", line 203, in flush
    self.logFile.flush()
RuntimeError: reentrant call inside <_io.BufferedWriter
name='/root/.local/share/backintime/takesnapshot_.log'>