Found reason for random mainwindow resize

[Alexander Dymo]

>> The reason is that the backgroundparser parses the file while parsing
>> and fails - as the statement is not finished. It then displays a red  
>> message in the
>> status bar to state that.
> Plugins should have standard ways to interacting with the UI and stop
> accessing the main window or dialogs...

Well, yes, but in this case writing a statusbar message is ok.
Mainwindow should be able handle long lines. I'll take a look.