Adding progress bar to status bar causes other panels to go black

I have an application, where I have added a progress bar to the status bar. I started to notice, that when I launch the application and at the same time activate some other window, covering the area where my application will appear, and keep it in focus, so that when my application is up, it will be behind this window, all the status bar panes (toolstriplabels) will go black and refuse to refresh... At the same time their background property stays "control". If I remove the progress from the statusbar and repeat all the steps, panes will be normal.

I tried calling Invalidate() on each pane and then Refresh() for the dialog - no result. Also I tried calling Activate() and Focus() from both constructor and Load handler - the same - no result... :(

Any ideas how to fix that?

Thanks