Ken S. said:
I created a new, empty game to test (5E sheet, defaults taken). After repeated trials, the problem appears to be intermittant. Sometimes I get a phantom waypoint, sometimes I don't. When I do, it's always caused by use of "x" to redisplay a measurement made with the measurement tool, not from token movement (then again, I didn't test token movement as much as I did measurement, as it wasn't causing any phantoms)
Steps:
open measurement tool
click-drag and right-click to add one or more waypoints, release left mouse to dismiss path
close measurement tool, open measurement tool (I never got a phantom if I didn't first close and reopen)
click x to redisplay last measurement
click anywhere to dismiss displayed path, sometimes a phantom of the first waypoint remains as illustrated above
When it does, it appears on both player and DM maps (I do have "broadcast to others" selected), but it's the player's color only on the player's map, on the DM's map it appears white
Further measurements will not erase it, each person has to exit and re-enter to remove their phantom
Both DM and test user are using a mac (separate macs), firefox, no extensions, and both cleared cache before launching the game to make these tests.
Note: while there's a token on the map, since I was also testing token movement, it appears to be irrelevant, and was not selected during the tests that created phantoms. And I'd exited and cleared cache after the token movement tests, before the tests that showed intermittant behavior.
We had this issue yesterday in our game. We have seven people in our game (including the GM), and use a variety of browsers and operating systems, so I'm pretty sure it's not related to browser or OS. The only way we found to get rid of the phantom boxes was to either reload roll20 or switch maps. With seven of us measuring stuff out we ended up having to reload at the end of every combat turn.