ofDisableDataPath() cause ofFile::openStream() error

Append mode use default para bRelativeToData = true

switch(_mode) {
        case WriteOnly:
        case ReadWrite:
        case Append:
            ofFilePath::createEnclosingDirectory(path());
            break;
        case Reference:
        case ReadOnly:
            break;
    }

//
static bool createEnclosingDirectory(string filePath, bool bRelativeToData = true, bool bRecursive = true); 

Start by tracing ofFile::openStream() into the append-mode branch and inspect how ofFilePath::createEnclosingDirectory() uses its bRelativeToData default. Reproduce the reported error with append mode and ofDisableDataPath(); done means the stream opens correctly without resolving the enclosing directory relative to the data path.