When you pass in false into the function GeoDataLineString::setTessellate in GeoDataLineString.cpp lines 478-493, it can actually set tessellation on instead of off. This happens because the function is using a xor operator when it should be using an and operator. See below:

    if ( tessellate ) {
        p()->m_tessellationFlags |= Tessellate;
        p()->m_tessellationFlags |= RespectLatitudeCircle;
    } else {
        p()->m_tessellationFlags ^= Tessellate;
        p()->m_tessellationFlags ^= RespectLatitudeCircle;
    }

The above should really be the following:

    if ( tessellate ) {
        p()->m_tessellationFlags |= (Tessellate | RespectLatitudeCircle);
    } else {
        p()->m_tessellationFlags &= ~(Tessellate | RespectLatitudeCircle);
    }