Checksum failure involving AES encryption

I've been working on an external tool to decrypt the contents of ODF 
containers, but two files in the container consistently fail their 
checksum when decrypted with AES256, even though they actually decrypt 
perfectly; the other files have no issues with their checksums. I have 
been trying to crawl the LO code for hints (esp. 
package/source/manifest/ManifestWriter), but am having some difficulty 
understanding the finer points of the code. Could someone more familiar 
with it have a look at this, please?

The problematic files in the ODF container are "manifest.rdf" and 
"Configurations2/accelerator/current.xml".
Only their checksum fails, the data actually decrypts just fine. Other 
files in the container have no problems.
The failure happens only with AES-encryption (no issues when using the 
Blowfish cipher).

I have not counted out the possibility that I'm doing something 
tremendously stupid, but it does seem like a bug in LO to me, and it 
would seem to have appeared with the introduction of AES.

For what it's worth, source to my Java tool/library is at 
https://github.com/kuschuermann/rltodfjlib
A ready-to-run binary (for Java 1.6+) is at 
http://ringlord.com/rltodfjlib.jar
Running it with "java -jar rltodfjlib.jar -v TestAES.odt" will dump 
useful information to the console.

Many thanks!

--Udo.