Wow! I struggled for hours, came here to report this problem and found this thread. I am on 2.7.2 CE and haproxy-devel 0.63_2. devel and non-devel packages have the same version (strange) but different dependencies. First I thought I made a mistake installing devel but it looks like the non-devel package has the same problem.
My findings are exactly as @safe's. I can only add that after I restart the haproxy service I can see in stats that the "backend" line of my backend shows something like 15s UP but the associated "MyBackendName" line shows something like 8m 23s UP, as it was never killed and restarted.
The workaround I found is to clone the backend, delete the old one and rename the new and double-check the frontend but I will try @safe's workaround that seems a little easier.
Since this hasn't gained attention since Feb. last year, how can report this to the developer?