getOpenFileName() crashes the app under Irix 6.5

We develop an in-hour app with Qt for deployment to multiple platforms. The app works fine under Windows, Linux. Unfortunately under Irix 6.5 (MIPSpro 7.4.2m), the app crashes whenever the file open dialog (via getOpenFilename() function) is opened. We find the culprit may be that there are too many files and directories (2000 or so) under certain directory, and the app crashes when this directory is nagivated to. We originally use Qt 4.3.0 and later try 4.5.0 but this issue remains.
To narrow down the scope of the bug. We tried a simple example program called mainwindow from chapter 3 of the book <<C++ GUI Programming with Qt 4>> by Jasmin Blanchette and Mark Summerfield. The issue still exists. So this might be a Qt bug.
To help to reproduce the bug, I attach the mainwindow source code. Please uncompress the tarball file and issue the commands follows:
$ cd QtExamples/chap03/mainwindow
$ qmake mainwindow.pro
$ make
$ mainwindow
Select the File, Open menu item to open the 'File Open' dialog box and navigate through the file system. Then the program would crash.