[OS X TeX] Undo after compilation?

[Jung-Tsung Shen]

A sympton I encountered the other day with TeXShop:

I made some minor changes in the manuscript, then had it compiled.
After the compilation, I clicked on "Undo" from the drop down menu,
and then tried to compile again (by clicking on the "typeset" button
within the editor), but the document refused to be compiled. Tried a
couple of other documents and they all behaved the same. I had to
close the document and reopened to proceed.

Is it true that you can't undo after the manuscript is compiled?

JT

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