Model automatically UnDo(es) last operation upon save

Running 2021 Studio on a W10 machine.

I am encountering a bug when I preform any Save of my model: SU UnDo (es) the last operation I did upon the save.

To avoid lost work, I add a random line to the model (which goes away upon saving). If I save the model again immediately, the last operation I did UnDo (es) anyway.

This happened in a model I was working on a few months back. I ended up doing a clean install and it was fixed. But I prefer not to have to do a clean install and reinstall all extensions again.

The bug persists if I close the model and reopen it. Previously, the bug “seemed” to extend to other existing models (hence the desperate move to do a clean install). Currently it only seems to effect this one model.


Upload your problematic model here if it is less than about 15MB, or if it is bigger, share it via Dropbox, OneDrive, WeTransfer or other file sharing service and post a shared link here.

That is very strange behavior. I wonder if there is some extension that is getting triggered when a Save is performed, and the extension is modifying the model?

The undo/redo stack is cleared when you save a SketchUp model, but I’ve never encountered the problem you describe. LIke @TDahl I wonder if some extension is responsible. You could try disabling them to see if that changes the behavior. If not, please do as @john_mcclenahan requested and share the file so we can investigate.

Really?!? When was such a horrid “mis-feature” added to SketchUp? I guess that’s another reason I’m glad to still use 2018 (despite having perpetual licenses up through 2021).

That doesn’t happen on Windows. I regularly use Undo after saving a model file and it works fine.

No - that should not happen. If that happens to you, try with extensions disabled.

My mistake! Sorry! The modified flag is cleared, but the undo/redo stack isn’t. Just to be sure I haven’t (completely) lost my mind, isn’t it true that undo/redo isn’t saved in a skp file?

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I made the same mistake a couple of days ago.
I haven’t noticed the undo stack surviving after a file is closed and reopened. If it did, I see interesting things happening if a file is closed without saving…

I don’t think that the Undo stack is saved in an SKP file. The Undo stack content is purely in the memory of the running SketchUp process (and is wiped from memory if the model is closed).

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Random thought…
You are working on the .SKP file ?
If you are [somehow] opening the .SKB backup file, then that will always be one save behind the SKP ??

Correct. It’s in-memory and atm holds 100 actions.

To go back to the original problem, what extensions are installed?

this is the original poster. Sorry for the slow response. I had this window open to watch the responses, but I was not reloading it (so it was static).

I’ll try to eliminate some components to make the model smaller. Maybe a screenshot of the extensions (?). I have never posted before, and am not quite sure how to upload a model, but I suspect I’ll figure it out.


I eliminated almost everything in the model. But the size is still substantial. There must be something stealth?

Go to Window/Model Info/Statistics and click the Purge Unused button, then ‘Save as’ something different so you can compare with the original.

Screenshot - 3_19_2022 , 8_46_48 PM

As Box indicated. Purge unused stuff. Deleting components from the model space doesn’t remove them from the file. Same with materials. File size is reduced by 99.96% after that.

Original poster here:
Performing what Box and DaveR suggested not only reduced the size of the file/model, but it also eliminated the problem with the Undo-on-Save.

I can only guess that there was some component (possibly a material imported with a component from 3DWarehouse) that was causing the problem. I don’t know what component it was, but maybe I can start with the full model before I “deleted” objects and components, and start to systematically delete and then purge-unused to maybe by brute force figure out what was causing the problem.

Since your model was quite complex and filled with unused components and materials, I wonder if you hit the size limit of the undo/redo stack.

I narrowed it down to this single grouping.
I downloaded a washing machine from 3DWh and copied/pasted to create a pseudo-combo. I might have resized them. The eventually grouped them.

So after all the elements in the model causing the Undo, it was the washing machine that was continually trying to remove a stain?
sku-comm-5.skp (534.5 KB)