Cannot reproduce with `kdesrc-build zxing-cpp --refresh-build`. I am getting:

```
 <<<  Build Process  >>>

Building zxing-cpp (1/1)
        Source update complete for zxing-cpp: no files affected
          Rebuilding because the option refresh-build was set
        Preparing build system for zxing-cpp.
        Removing files in build directory for zxing-cpp
        Old build system cleaned, starting new build system.
        Running cmake targeting Unix Makefiles...
        Compiling... succeeded (after 10 seconds)
        Installing zxing-cpp succeeded (after 0 seconds)

```

The warning you see is from this code:
```perl
        # Check to see if we're actually supposed to go through the
        # cleaning process.
        if (!$self->getOption('#cancel-clean') &&
            !$buildSystem->cleanBuildSystem())
        {
            warning ("\tUnable to clean r[$self]!");
            return 0;
        }
```

The cleanBuildSystem return hint:
```
# Returns 0 for failure, non-zero for success.
sub cleanBuildSystem
```

The 0 status at revision you mentioned happens only after the `error (...)`  message is shown, but you have not that printed.
If the issue still happens to you, please provide more details.