Link activities by drag & drop from Planning (gantt) view works only once

Version 5.0.5
Can be reproduced on Firefox (not tested on other browsers)
Linking two activities by drag & drop on gantt view works the first time, but not any more after that (the link appears graphically on the gantt, but no relation is persisted in database).

Ok, I could reproduce (after a number of retries) on demo project (see attached screen copy that show graphically the link between activities on Gantt view while nothing is persisted in database).
It looks that I had to first assign some time to previous activity to reproduce the problem.

EDIT : I (re)tried to reproduce but did not succeed this time on demo environment. It is though very easy to reproduce on my environment. I noted that my projeqtor environment is way slower than the demo one is (projeqtor installed locally on top of easyPHP). Might be linked ?

I think I finally understood how to reproduce the problem : it occurs when the "drop" is done on the right of the green rectangle representing the task (on the name of the resource for example). Easy to reproduce especially on "small" tasks.