Bug during Merge Test (Subversion Exception)

During merge test Subversion Exception appears:
In file
'D:\Development\SVN\Releases\TortoiseSVN-1.6.1\ext\subversion\subversion\libsvn_client\mergeinfo.c'
line 970: assertion failed (pb != NULL)

How I get this message:
1. Create repository in c:\JacekQ\Repozytorium\SVNTest.
2. Checkout this repository to c:\JacekQ\Projekty\SVNTest.
3. In Working Copy add folders and source file:
- c:\JacekQ\Projekty\SVNTest\branches
- ...\tags
- ...\trunk
- ...\trunk\ProjektTestowy (project folder)
- ...\trunk\ProjektTestowy\program
- ...\trunk\ProjektTestowy\program\prg1.c
4. Commit c:\JacekQ\Projekty\SVNTest.
5. Delete folders c:\JacekQ\Projekty\SVNTest\*.
6. Checkout repository c:\JacekQ\Repozytorium\SVNTest to c:\JacekQ\Projekty\SVNTest.
7. Create tag SVNTest\tags\ProjektTestowy_1.00
8. Create branch SNVTest\branches\ProjektTestowy_1.01
9. Modify prg1.c in branch.
10. Merge branch with trunk.

I save all files from repository\SVNTest, Projekty\SVNTest.
If you need some of them just tell me the names.

Best regards,
Jacek Kucharzyk