I can provide sample code to reproduce this bug encountered with a MIDP2 application on Nokia 5800 that uses complex and simple JavaME forms.
By "complex forms" I mean standard javax.microedition.lcdui.Forms with more than 5-6 standard JavaME components (Choices, TextFields, etc.).
I found that calling "Display.getDisplay(midlet).setCurrent(form);" even in a user-initiated thread (distinct from the event-management-thread)
causes the application to exit unexpectedly to the phone Applications menu, instead of showing next screenful. No notification is given: JVM crashes.
I tested thoroughly and found no memory leaks, Stack overflows or deadlocks: the issue shows even with a very simple midlet with 2-3 forms with no network/bluetooth/etc. activity.
Java version: all (built-in, Java Runtime 2.0.1 and 2.0.2)
Firmware NOKIA5800Xm: 30.0.011