Is Browning Suppose to Occur Every Time After IPL?

As some of the other practitioners have pointed out, IPL may not be the best choice for textured (bumpy) acne scars. It sounds like you are being treated for pigmented acne scars. For pigmented (dark) acne scars, IPL is one choice, there are also two others:

Hydroquinone bleaching creams.
Q-switched laser treatments (for faster results then IPL)

One possible reason why you experienced some "Browning" and flaking that occurred after the treatments is because the contrast between the color of the scar and the color of the skin is great. As the scars fade, the color of the scar and the color of the skin are closer to the same and in the case, the browning and flaking you discussed will be less noticeable or not occur at all. Lasers and light devices work by focusing light energy on the darker areas so lighter the spots, the less they respond.

IPL might not be the best option for treating acne scars. A lot of times acne, can leave a dark mark or pigmentation spots on the skin. In this case, IPL will work but only to lighten the pigment, not to smooth out the scars. Fraxel will be a better choice to improve both- the scars and the pigment at the same time. After IPL, darkening suppose to occur but only for the first 1-2 treatments. After each time you will have less and less pigment which means less target for the laser, therefore less browning.

Initial IPL treatment of hyperpigmentation produces browning that flakes off.  As the colour fades higher energies are required as less energy is absorbed.  Browning does not occur every time.  IPL can still work but is less effective.

IPL may not be the best choice for acne scars. It usually is good for sun spots or redness of the skin. 

Fraxel is a better choice for acne scars. Most people feel the carbon dioxide fractionated lasers are superior to the erbium variety. Of course, the gold standard for laser resurfacing is still the pulsed CO2 lasers but few physicians venture in using them due to the high complication rate.
The fact that you are not getting the browning and flaking anymore from the IPL is normal. This means the IPL has done about the best it can do in removing the pigment. The IPL light, forgive the redundency, is attracted by the brown pigmentation, If there is now scant brown pigment left , there is going to be less of an effect.