Apple has handed developers the fourth beta of Mac OS X 10.6.5, the upcoming maintenance update for the company’s Snow Leopard operating system.

Packing pretty much the same code as the previous build, Mac OS X 10.6.5 10H535 is 570MB in size for the delta update.

Particularly, the build contains six focus areas and the same known issue affecting USB devices when virtualization software is installed.

This time around, however, both VMware and Parallels are mentioned.

According to World of Apple, which was able to obtain the actual seed notes for the build, Apple did not include a list of applied fixes, the same as with the former seed.

Therefore, the seed notes look as reproduced below:

Known Issues
- Having VMware or Parallels installed may prevent USB devices from being available

Focus Areas
- 3D Graphics
- iCal
- Mail
- QuickTime
- Time Machine
- USB Devices

Apple is believed to plan the Mac OS X 10.6.5 public release soon, with development appearing to unfold without problems.

Moreover, a short successions of seedings, such as the one we’re witnessing with 10.6.5, has indicated in the past that development is wrapping up.

Still, Apple always needs to iron out all of the known bugs before rolling out a system update, therefore the issues with installed virtualization software are keeping the update in testing.

Some issues are harder to fix than others, making it impossible to estimate a timing for the OS X 10.6.5 release.

For comparison, Mac OS X 10.6.4 spent about two months in development and was released in June.

It included Safari 5 and the usual bag of general operating system fixes that enhance the stability, compatibility, and security of Macintosh computers.

Notably, 10.6.4 resolved an issue that could prevent some Adobe Creative Suite 3 applications from opening.

The software update, however, also came with a few incompatibilities with NVIDIA graphics, resulting in bad behavior with some video games.

These problems have since been addressed via the Snow Leopard Graphics Update released by Apple last month.