Win32 defines a graphics batching model whereby simple API calls that
only return a success/failure code can be batched indefinately on a
per-thread basis. This leads to problems where threads will often
have a number of unexecuted graphics primitives in their queues that
remain there indefinately and which can reappear at inopportune times
(such as after a new on-screen context has been established and an old
drawing suddenly appears on it).

This model is only really implemented on Windows 3.51, it appears that
Windows 95 does not do any batching and gets its performance gains in
other ways. Turning off the batching for every thread on Windows 3.51
can drastically affect its performance. Also, ensuring that all threads
have batching turned off is difficult since the command to disable batching
must be executed by each thread. In order to be fully sure that batching
was disabled, the command to turn off batching would have to be executed
by the Java interpreter runtime, thereby creating a dependency on the
GDI from the non-graphical runtime dll's.

The HotJava application is rather strikingly impacted by this problem where
elements of one HTML page will be drawn on top of another page after the
user has switched pages.