voting on session proposals unreliable on windows 10, edge

[mrtopf]

When clicking on the vote button on a session proposal with e.g. edge on win10 sometimes nothing happens, sometimes it directly switches back.

It should reliably vote or unvote instead.

[jonasstein]

Same on Firefox 65/Linux. I tried to vote PythonCamp proposals, but the icon just flickers and reloads the old value. This is reproducible for all proposals. Is there any workaround for Linux/Firefox?
Update: I managed somehow to vote for one proposal, but the effect remains the same for all others.