Qt SDK commercial fails to install because of isufficent disk space

When using the Qt SDK commercial package the installer fails claiming insufficient HD ( true of /), when the desired install path /usr (probably /usr/local/Qt/4.5.2/ ) has
plenty of available space.

It does not even suggest where it is going to install to prior to giving
the error. Install directory choice should be made before a check for sufficent space.

look at the change between the opensource installer and the commercial
installer-

O1- Welcome to the Qt SDK Setup Wizard...
O2- Please read the following License Agreement...
O3- Please specify the directory where Qt SDK will be installed.
O4- Select Components...
O5- Setup is now ready to begin installing Qt SDK...

from what you described above, the commercial version has a different
order:

C1- Welcome to the Qt SDK Setup Wizard...
C2- Select components...
C3- Please enter your Qt license key...(entered your licence info)
C4- Please read the following License Agreement...
C5- Please specify the directory where Qt SDK will be installed.
C6- Setup is now ready to begin installing Qt SDK...

Both appear to check for disk space at the end of the Select Components stage (O4 and C2); I tried the open source Installer and it gave me the insufficent disk space message after O4 if I used the default directory. The issue is that if you check for adequate disk space between C2&C3, you don't know where you are really installing it to- leaving you with 2 logical problems-

a) my case- not enough space in the default dir -fails improperly; there
is space in the true install dir, but no space in the defauinstall dir)

b) user selects non default dir with inadequate space- succeeds improperly;
will fail when it tries to install...

I have created a workaround/bug demonstration:
Create a loopback FS for / opt that is either big enough or too small-

a) dd if=/dev/zero of=/somewhere_that_has_space/opt_test.img bs=1M
count=sz_in_MB
b) /sbin/losetup /dev/loop0 /somewhere_that_has_space/opt_test.img
c) mkfs -t ext3 /dev/loop0

if there are no contents in /opt you need to preserve then you may
proceed to the install

d) mkdir /mnt/opt
e) mount -t ext3 /dev/loop0 /mnt/opt
f) cp -R /opt/* /mnt/opt
g) umount /mnt/opt
h) mount -t ext3 /dev/loop0 /opt

Install the sdk...

With a 2048 MB loopback file it succeeds; It fails for a 50 MB
loopback file.