Blinking powerline led means that the adapter is transferring data...That's normal...
Any problem with your internet connection?

Yes, it's very slow.
I see on one unit both the Powerline led and the Ethernet LED blinking, but on the other unit just the Ethernet LED.
I was expecting on both units the same LED behaviour since they both receive and transmit data.

Cheers,
Klaas

It is slow but you can access internet, right?
Did you install powerline utility? What's the rate?
Are they brand new? You may try to reset them and re-pair.
http://www.tp-link.com/en/faq-312.html
http://www.tp-link.com/en/faq-258.html

This is the explanation for the LEDs:

http://www.tp-link.com/en/faq-432.html

Try resetting back to factory:

http://www.tp-link.com/en/faq-312.html