Low Priority: When add many instances get exception

[MrSteve]

This is low priority I am guessing folks are preparing for Scratch conference, but wanted to make sure I recorded this.

To re-create:
1) open attached project
2) hit <space> key and enter 10

The exception seems to occur if you enter any value above 8, lower values work fine.

Bug occured on Mac using V53 build.

I'll try and test some more later and see if I can come up with a simpler example of the issue
PS tested some more and issues seems intermittent.

[MrSteve]

See attached project which more reliably recreate the problem.

1) Open attached project
2) hit <space> key

Note this project works fine in V51