Created attachment 153773 [details]
Screenshot

If you run a Maven project, and it outputs a line consisting of a number followed by the letter "B", that line does not show up in the output window.

This appears to be due to the following code in org.netbeans.modules.maven.output.GlobalOutputProcessor:

/*test*/ static final Pattern DOWNLOAD = Pattern.compile("^(\\d+(/\\d*)? ?(M|K|b|KB|B|\\?)\\s*)+$"); //NOI18N
...
if (DOWNLOAD.matcher(line).matches()) {
    visitor.skipLine();
    return;
}

Clearly the idea is to avoid flooding the output window with maven's download progress output (which would take up many lines as the output window doesn't implement carriage returns), but it's not hard to write a program that outputs a matching line by accident. (I discovered this behavior when I wrote a program to list all the Unicode whitespace characters, and spent way too long trying to figure out why "000B" wasn't listed)

Assuming that handling carriage returns differently from line feeds isn't feasible, one way to make this filter less likely to hide legitimate program output might be to count the number of "Downloading: " lines minus the number of "Downloaded: " lines seen so far, and only hide lines when that number is positive.