svnadmin dump fails with E200020: Pathname not terminated by ':'

Hi list,
we have a quite old & grown svn repository here. With some "interesting"
svn:mergeinfo Properties. (see the diff below)

This seems to be been allowed in earlier svn versions.

For backup Issues svn copy worked fine for all the time,
but now we want to update our server (svn version & hardware) and
do a full svn dump/load cycle:

svnadmin dump --incremental -r 59979 src-100904/ > /root/src.dump
svnadmin: E200020: Pathname not terminated by ':'

As reading a little bit in the docs & code I found out that there is a
possibility to bypass the check on svn load (--bypass-prop-validation),
but not with svn dump.

It looks like we have mutliple Changes like this one.

Does anyone have suggestions how to get on with that issue?

Kind regards
  - Jan

Index: cdb/branches/sdkport
===================================================================
--- cdb/branches/sdkport (revision 59978)
+++ cdb/branches/sdkport (revision 59979)

Property changes on: cdb/branches/sdkport
___________________________________________________________________
Modified: svn:mergeinfo
## -1 +1 ##
-/cdb/branches/2.9.6:57323,57600
+57600
\ No newline at end of property

Some details:

root_at_oscar:~# svnadmin --version
svnadmin, version 1.7.8 (r1419691)
   compiled Dec 11 2012, 15:36:32

Copyright (C) 2012 The Apache Software Foundation.
This software consists of contributions made by many people; see the NOTICE
file for more information.
Subversion is open source software, see http://subversion.apache.org/

The following repository back-end (FS) modules are available:

* fs_base : Module for working with a Berkeley DB repository.
* fs_fs : Module for working with a plain file (FSFS) repository.

root_at_oscar:~# cat src/db/format
3
layout linear
root_at_oscar:~# cat src/db/fs-type
fsfs