Version:           1.5.3 (using KDE KDE 3.5.2)
Installed from:    Debian testing/unstable Packages
OS:                Linux

Here is the testcase :

Create the following .h :

class KWQArrayImpl
OOM_MODIFIED
{
    class KWQArrayPrivate
    OOM_MODIFIED
    {
    };
};

Then import this code source in umbrello.
(OOM_MODIFIED is normally defined as ": public CObjectBase", but is obviously undefined here)
Double click on OOM_MODIFIED in the left pane (UML Model) : the application freezes, eating up all the memory.