Startup hangs loading drivers after manual installation of ATI Radeon 2600 graphics driver

See Core-16060: In ROS 0.4.13 and at least version 0.4.14-dev-1238 it was possible to manually install the ATI Radeon 2600 graphics driver on my HP Compaq 8510p notebook with following steps:

• Install VC++6 via ".inf" file
• Install 7zip
• Deflate ATI Radeon 2600 driver setup
• In device manager, point graphics card to use driver in "\Driver\XP_INF" subdirectory
• After a reboot ReactOS would show the desktop in native resolution, albeit without icons.

Tests with newer ROS revisions show a regression, preventing a successful reboot after the driver installation. ROS will hang forever loading ATI2MTAG.SYS itself (=result with 0.4.15-dev-4853-g3a72a52 ).

Note that the test for 0.4.15-dev-4853-g3a72a52 was done using a patched version of ntoskrnl.exe because of CORE-17879, just in case this is relevant.

Here are screenshots of the backtrace/Dmesg for 0.4.15-dev-4853. I hope they help:

According to Serge Gautherie the 0.4.15-dev-4853 callstack points to videoprt.