[dev mar 6, also release 3.3.1 same] If you create a PropertySheet
instance outside the event thread - I think it may need to be from the
request processor - set a node with some properties using setNodes,
then display the sheet in e.g. a NotifyDescriptor dialog: no
properties are shown (the "<no properties>" empty panel appears). If
created from the event thread, the node's properties are displayed
correctly.

I believe this is a bug, since generally it is OK to construct Swing
components from any thread, provided they are only displayed from the
event thread, and only manipulated when visible from the event thread.
If this cannot be easily fixed for PropertySheet, please document in
its constructor that it ought to be called from the event thread;
and/or throw an IllegalStateException from the constructor if
!SwingUtilities.isEventThread().

To reproduce: comment out the event-thread check from
innertesters/src/org/netbeans/modules/innertesters/InnerCompilerType.java
in the beginning of the method warn(String). Now create a build incl.
at least innertesters and java modules. Create from template a
Classes/Unit-testable Class and try to compile it. You will get a
warning that you have not set a base compiler. This might or might not
show the property sheet for the inner compiler type correctly. Close
the window with OK, leaving the compiler unset. Leave the testable
class open in the Editor and focused, and shut down and restart the
IDE. As soon as the main window opens, the Java module tries to
compute an out-of-date badge for the class -> the compiler type is
used -> a warning is displayed. This will show no properties. However
pressing F9 after that to compile might show it correctly. If the
event-thread check in InnerCompilerType.warn is readded, the
properties always appear in the dialog.

Attaching a test patch to PropertySheet which shows what it is doing.
With or without the fix in InnerCompilerType, a reasonable sequence of
steps is shown in the log file:

PS.RN.postNodes: nodes=[]
PS.RN.postNodes: nodes=[<ITC bean node>]
PS.RN.run: nn=<ITC bean node>
PS.RN.run/run: nn=<ITC bean node>
PS.rPS: node=<ITC bean node>
PS.rPS: p=[Lorg.openide.nodes.Node$PropertySet;@50005e
PS.rPS: p[0]=Properties
PS.rPS: adding pages

So the emptyPanel is added in the constructor in the request
processor, and apparently then later removed and replaced with the
tabbed pane with one property from the event thread. But just the
emptyPanel is displayed nevertheless.