Einstein light clock? In light clock thought experiment,if the observer is moving with velocity v relative to the light source&mirror frame ,then why path of light bends?
According to einstein's postulate speed of light is independent of source motion??  
 A: 
.... why path of light bends? According to einstein's postulate speed of light is independent of source motion??

Because "bending" is a second order notion. You have to know at least the second order terms of a function's Taylor series to know whether it is linear or nonlinear. You can't tell whether a function is nonlinear if you measure its changes over a subdomain wherein a linear approximation is better than your measurement accuracy.
On the other hand, the constancy of $c$ is a local notion; it says that, as long as your measurements are made in a domain with small enough extent in space and time that the spacetime manifold is well approximated by its tangent space, i.e. approximated by the best fit Minkowski spacetime approximation than to within a deviation smaller than your measurements can detect, then the maximum speed of propagation of a signal, or the speed of propagation of any massless particle (such as one of light), will be $c$. 
You have to measure over a spacetime domain broad enough that the second derivatives of the metric can be detected to detect bending of light. Indeed, if one chooses so called Riemann normal co-ordinates, one can write the metric in terms of the Riemann tensor as:
$$g_{\mu\nu} = \eta_{\mu\nu} - \frac{1}{3} R_{i\,k\,j\,\ell} X^k\,X^\ell + O(X^3)$$
where $\eta = \mathrm{diag}(1,-1,-1,-1)$ is the Minkowski metric and our local laboratory is the same as Minkowski spacetime, to first order in the tangent vector (approximating the displacement from the origin) $X$. This equation gives yet another intuition for the Riemann tensor, as a fundamental "encoding" of the lowest order non-Minkowski behavior of the spacetime manifold.
A: Only the speed of light is constant in special relativity , so the direction can be affected by the motion of the source.
