System Info:
Looking for user plugins in C:\Documents and Settings\Administrator\Application Data\MySQL\Workbench\plugins
MySQL Workbench OSS for Windows version 5.0.25
Cairo Version: 1.5.12
Rendering Mode: GDI Rendering
OpenGL Driver Version: Not Detected
OS: Windows Server 2003/XP
CPU: 4x Intel(R) Core(TM)2 Quad CPU    Q6600  @ 2.40GHz, 6.0 GB RAM
Video adapter info:
Adapter type: ATI Radeon HD 2900 XT
Chip Type: ATI Radeon Graphics Processor (0x9400)
BIOS String: 113-B00701-101
Video Memory: 1048576 KB

A black mouse cursor shows that the left mouse button is pressed.

Test 1:

Test1/Test1_1.png (left mouse button pressed)
Test1/Test1_2.png (left mouse button pressed; mouse moved one pixel upwards; Diagram should move but haven't done it)
Test1/Test1_3.png (left mouse button released; Diagram shouldn't move now but have done it)

Test 2:
Test2/Test2_1.png (left mouse button pressed)
Test2/Test2_2.png (left mouse button pressed; mouse moved one pixel upwards; Diagram should move but haven't done it)
Test2/Test2_3.png (left mouse button pressed; mouse moved one pixel downwards; Diagram moved in the wrong direction [downwards], because it is one move behind)
Test2/Test2_4.png (left mouse button pressed; mouse moved one pixel upwards; Diagram moved in the wrong direction [upwards], because it is one move behind)
Test2/Test2_5.png (left mouse button pressed; mouse moved one pixel downwards; Diagram move in the wrong direction [downwards], because it is one move behind)
Test2/Test2_6.png (left mouse button pressed; mouse moved one pixel upwards; Diagram moved in the wrong direction [upwards], because it is one move behind)
Test2/Test2_7.png (left mouse button pressed; mouse moved one pixel rightwards; Diagram doesn't moved and is one move behind)
Test2/Test2_8.png (left mouse button released; Diagram moved downwards)