Inserting a block sometimes results in movement on the workspace

[microbit-robert]

Sometimes, inserting into a block or stack results in unexpected movement of the entire stack. In the example below, everything shifts to the right hand side (potentially off-screen for many users). At this point, pressing "Enter" to accept the current position of the newly inserted block removes that block from the workspace. There are no logged errors in the console.

I cannot reproduce this reliably, but I've now observed it several times.

insert-bug.mov

[rachel-fenichel]

Are you still seeing this? And if yes, do you have a repro case?

[microbit-matt-hillsdon]

We can't reproduce this. Perhaps it was related to #604