Disconnecting a running stack leads to broken behavior

[ericrosenbaum]

Expected Behavior

Clicking a running (highlighted) stack should always stop it.

Actual Behavior

If you disconnect a running stack, so that e.g. a forever loop is running in the detached part, and then click the still-running fragment, it does not stop. Instead, there are now two "copies" of the stack running in the VM (for example, if the stack causes a turn of 10 degrees per frame, it will now turn 20 degrees per frame). Clicking again stops and re-starts this second version, without affecting the first.

Steps to Reproduce

• Run a stack including a forever loop in it
• Detach the part containing the forever loop, which stays highlighted and running
• Click the detached stack. Note that it stays highlighted, and is running "twice", so e.g. its side effect is occurring twice as fast.
• Click the detached stack again. Still highlighted, running "once".