@nibbe: At least this part " ... and only by saving ica-file and launching that from command line. ..." can be solved by these steps 7 - 9:

7. vi /etc/profile insert 'export ICAROOT=/opt/icaclient' in the line below of 'export PATH...'
8. cp /opt/icaclient/npica.so /home/user/.mozilla/plugins/
9. reboot

from http://talk.maemo.org/showthread.php?t=32699&page=3

At least, this worked for me but did not resolve the empty or black window issue.