Descriptive Problem Summary:
Client crushes when secondary window with screen is closed. It also crushes when the screen in popup window is deleted.

Numbered Steps to Reproduce Problem:
Sorry for not having minimal test case. Here is a test case that will reproduce this issue consistently https://files.catbox.moe/7wdd5b.zip (150mb)
1. Open the .dme in DreamMaker on 516.1655 (or any 516)
2. Compile + Run (trusted is not required)
3. Allow the game to boot.
4. Click the observe button and confirm.
5. Use the "Abc-Crush-Reproduction" verb in the input in the bottom right (the code being executed is identical to the snippet below).
6. Close the window
7. Game closes?

If minimal test case is required please let me know and I'll try to come up with something.

Code Snippet (if applicable) to Reproduce Problem:
Not applicable


Expected Results:
Window closes, game continues.
Actual Results:
Client crushes
Does the problem occur:
Every time? Or how often? Yes
In other games?
In other user accounts?
On other computers?

When does the problem NOT occur?
On version 515.1647 but I suspect this is due client versions checks in codebase.
Did the problem NOT occur in any earlier versions? If so, what was the last version that worked? (Visit http://www.byond.com/download/build to download old versions for testing.)

Workarounds: