Mirror inputs, "Return Atom" button becomes visible at different times

[phet-steele]

In the Mirror Inputs wrapper of 1.2.0-rc.2

1. Interaction screen
2. Pause!
3. Force the atoms together
4. Hold down the step forward button, but start to be careful as the atom approaches the edge of the screen

You'll notice, by stepping slowly, that the "Return Atom" button appears on the bottom sim first:

Clicking in the top sim where the button would be will click the button in the bottom sim, leading to desynchronization.
Based on #325 (comment), I doubt this issue needs to be addressed before the delivery of 1.2,

Seen on Win 10 FF 80 For phetsims/qa/issues/531.

[arouinfar]

Discussed with @jbphet and @kathy-phet. We decided that this does not block the 1.2.0 release. @jbphet will take a look at this to see if it's symptomatic of a larger problem.

[zepumph]

I feel quite sure that this is the exact same problem as #325, since that was a general issue about Randoms getting out of sync. @phet-steele can you please confirm this is fixed on master. If this is the case, then cherry-picking changes for #325 will be enough, and this only needs to be confirmed fixed as a result of those changes.

[jbphet]

Unassigning until the maintenance release is designated as one of my priorities.

[phet-steele]

I checked and doubled checked (by pulling repeatedly) that master on phettest had the changes listed in #325 (comment).

I, however, still see this issue on master.