Manual CellGrouping option causes crash at cell evaluation

Question

Update: Try to reproduce this behaviour with CellGrouping set to manual. To do that:

either evaluate SetOptions[$FrontEnd, CellGrouping -> Manual],
or hit CTRL+SHIFT+O to bring up the Option Inspector window, Lookup (among Global preferences) the option CellGrouping and set it to Manual.

Please test whether the phenomen is reproducible for you with the changed setting. You can reset cell grouping to its default behaviour by:

SetOptions[$FrontEnd, CellGrouping -> Automatic]

Strangest bug ever. Copy the following piece of code to the same notebook two times, below each other, as two identical cells. Be sure to run a fresh kernel.

DynamicModule[{x}, Print[1]; Dynamic@x, Initialization :> Print[2]]

Now evaluate the second cell. Fine, it returns and prints stuff.

Mathematica graphics

And now, without quitting the kernel, evaluate the first cell. It crashes Mathematica. Every time, and only when the first cell is evaluated. If (after a restart) I only evaluate the first cell, Mathematica crashes again.

How come that the outcome of evaluating two identical cells depends on whether the cell is the last one or not?

Furthermore, this one causes a crash on its own:

DynamicModule[{x}, Dynamic@x, Initialization :> Print[2]]

Mathematica 9.0.1.0 Windows 7 (64-bit), no packages, problem persists after full reboot, suggestion bar is turned off.

No crash here. works fine. please say which platform and version you are using when reporting possible errors. I am on windows 7, 64 bit, V 9.01 — Nasser, Dec 06 '13 at 14:55
Can't reproduce it in 9.0.1 on Windows 7 x64. The FE code differs substantially between platforms--which one are you on? — Oleksandr R., Dec 06 '13 at 14:56
Does not crash (MMA 9.0.1 Win7 64). Although I find it a bit strange that 1 gets printed before 2:) — Ajasja, Dec 06 '13 at 15:23
@Ajasja You shouldn't: Initialization code is only evaluated after the return value of the DynamicModule is displayed (see here). — István Zachar, Dec 06 '13 at 15:35
@IstvánZachar not at all, depending one what you mean by crash. — Öskå, Dec 06 '13 at 15:41
Are you saying (looking at your figure) that none of the Print statements get printed on your machine? They do get printed, I just happened to have changed my preferences to send Print output to the console window. They did go there, I saw the prints on the console. — Nasser, Dec 06 '13 at 20:44
@IstvánZachar, same story for me with the first DynamicModule. Now the second one does crash. — Öskå, Dec 11 '13 at 10:57
Well, apparently I'm like the only one with you to have issues. If you got further tests you can ping me in chat if you want to :) — Öskå, Dec 11 '13 at 12:13

István Zachar · Accepted Answer · 2013-12-16T19:14:39.913

Tech Support kindly answered and acknowledged the crash:

The crash is now reproducible after setting the option CellGrouping -> Manual. I have forwarded it to the developers for further investigation. You will be informed when a fix is made available.

You can turn off manual CellGrouping with:

SetOptions[$FrontEnd, CellGrouping -> Automatic]

Also, restarting Mathematica in clean mode resets everything including cell grouping behaviour to defaults and the two cells behave normally. The documentation states:

mathematica.exe -clean: ignore stored caches and rebuild the front end preferences file

(It also seems like from the documentation that this is a Mac-only option, but it also applies to Win.)

Manual CellGrouping option causes crash at cell evaluation

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