merge disagrees with diff

We're having a major problem with subversion, it seems that for some
changesets svn merge will do a different change than svn diff would
suggest.

Here's an example of that the problem looks like:

svn diff -c 648291 svn+ssh://myserver/somepath/stepws.xsd

Index: stepws.xsd
===================================================================
--- stepws.xsd (revision 648290)
+++ stepws.xsd (revision 648291)
@@ -366,6 +366,37 @@
     </complexType>
     <element name="getLOVValueIDsResponse"
type="tns:getLOVValueIDsResponseType"/>

+ <!-- getAssetSystemValues -->
+
+ <complexType name="getAssetSystemValuesRequestType">
+ <sequence>
+ <element name="accessContext" type="types:accessContext">
+ <annotation>
+ <documentation>username and password for the user
to access STEP as, and the URLs of the context and
+ workspace to access data through.
+ </documentation>
+ </annotation>
+ </element>
+ <element name="nodeURL" type="string">
+ <annotation>
+ <documentation>URL of the asset to obtain system
values from</documentation>
+ </annotation>
+ </element>
+ </sequence>
+ </complexType>
+ <element name="getAssetSystemValuesRequest"
type="tns:getAssetSystemValuesRequestType"/>
+
+ <complexType name="getAssetSystemValuesResponseType">
+ <sequence>
+ <element name="values" type="types:value" minOccurs="0"
maxOccurs="unbounded">
+ <annotation>
+ <documentation>The attribute values</documentation>
+ </annotation>
+ </element>
+ </sequence>
+ </complexType>
+ <element name="getAssetSystemValuesResponse"
type="tns:getAssetSystemValuesResponseType"/>
+

Now I tried to check out an older branch to backport that change:
> svn co svn+ssh://myserver/someotherpath
> cd someotherpath
> svn merge -c 648291 svn+ssh://myserver/somepath/stepws.xsd stepws.xsd
Conflict discovered in 'stepws.xsd'.
Select: (p) postpone, (df) diff-full, (e) edit,
        (mc) mine-conflict, (tc) theirs-conflict,
        (s) show all options: p
--- Merging r648291 into 'stepws.xsd':
C stepws.xsd
Summary of conflicts:
  Text conflicts:

> svn diff

Index: stepws.xsd
===================================================================
--- stepws.xsd (revision 610503)
+++ stepws.xsd (working copy)
@@ -366,6 +366,76 @@
     </complexType>
     <element name="getLOVValueIDsResponse"
type="tns:getLOVValueIDsResponseType"/>

+<<<<<<< .working
+=======
+ <!-- getAssetSystemValues -->
+
+ <complexType name="getAssetSystemValuesRequestType">
+ <sequence>
+ <element name="accessContext" type="types:accessContext">
+ <annotation>
+ <documentation>username and password for the user
to access STEP as, and the URLs of the context and
+ workspace to access data through.
+ </documentation>
+ </annotation>
+ </element>
+ <element name="nodeURL" type="string">
+ <annotation>
+ <documentation>URL of the asset to obtain system
values from</documentation>
+ </annotation>
+ </element>
+ </sequence>
+ </complexType>
+ <element name="getAssetSystemValuesRequest"
type="tns:getAssetSystemValuesRequestType"/>
+
+ <complexType name="getAssetSystemValuesResponseType">
+ <sequence>
+ <element name="values" type="types:value" minOccurs="0"
maxOccurs="unbounded">
+ <annotation>
+ <documentation>The attribute values</documentation>
+ </annotation>
+ </element>
+ </sequence>
+ </complexType>
+ <element name="getAssetSystemValuesResponse"
type="tns:getAssetSystemValuesResponseType"/>
+
+ <!-- addLOVValueIDs -->
+
+ <complexType name="addLOVValueIDsRequestType">
+ <sequence>
+ <element name="accessContext" type="types:accessContext">
+ <annotation>
+ <documentation>username and password for the user
to access STEP as, and the URLs of the context and
+ workspace to access data through.
+ </documentation>
+ </annotation>
+ </element>
+ <element name="nodeURL" type="string">
+ <annotation>
+ <documentation>URL of the LOV to obtain values
from</documentation>
+ </annotation>
+ </element>
+ <element name="add" type="types:lovvalueid" minOccurs="1"
maxOccurs="unbounded">
+ <annotation>
+ <documentation>The list of LOV values to
add</documentation>
+ </annotation>
+ </element>
+ </sequence>
+ </complexType>
+ <element name="addLOVValueIDsRequest"
type="tns:addLOVValueIDsRequestType"/>
+
+ <complexType name="addLOVValueIDsResponseType">
+ <sequence>
+ <element name="values" type="types:lovvalueid"
minOccurs="0" maxOccurs="unbounded">
+ <annotation>
+ <documentation>The new list of LOV values</documentation>
+ </annotation>
+ </element>
+ </sequence>
+ </complexType>
+ <element name="addLOVValueIDsResponse"
type="tns:addLOVValueIDsResponseType"/>
+
+>>>>>>> .merge-right.r648291
     <!-- getValuesByAttributeIds -->

     <complexType name="getValuesByAttributeIdsRequestType">

As you can see the resulting change to the checked out file after
merge is different from the change reported by diff.

I've found this problem on 1.6.12 and reproduced it with a
home-compiled 1.7.1, the server runs ubuntu server 10.10.

Clients are mostly linux with mostly 1.6.12, but there are windows
machines and 1.7.1 clients as well.

I did not find any --dont-merge-random-crap option, so I'm very confused.

-- 
Flemming Frandsen - YAPH - http://osaa.dk - http://dren.dk/