The button will only respond if there is a README for the installer in the first place. Which installer are you using that shows this problem? It could also be a custom glade file that lacks the proper naming in some widgets.

Of course there is README and as I wrote the README button works all the time except the installer is copying files. I checked and recognized I was not using the latest *glade* file from CVS. With them the problem disappeared, so this can be closed.

Thanks.

I thought the problem was gone with the latest *glade* files but this was a mistake.

You can view the Readme until pressing 'Begin Install' while it's installing files from a cd/dvd if the files which are installed are part of the installer (shipped with  the installer) you can open the Readme and also if the installer has finished copying files from cd/dvd or while the installer is waiting for the next cd/dvd. You only can not read the Readme while the installer is copying files from cd/dvd. I hope I described the problem more understandable this time.

Is this more prone to happening when big files are being copied from CD/DVD ? It is quite possible that the GTK event loop is not being processed often enough while a file is slowly copying, leading to the UI to be unresponsive. Or is it just not happening at all ?

It's just not happening at all and it dosen't matter if copying a big file or several small files from a disc.