RJ TextEd

I was editing a readme.md file. It had the following lines in it:
```
- expanding the specified file spec to a fully-qualified form
- handling UNICODE
- providing access to debug/info functions such as syslog() and get_system_message()
```
I changed these lines to:
<li>expanding the specified file spec to a fully-qualified form</li>
<li>handling UNICODE</li>
<li>providing access to debug/info functions such as syslog() and get_system_message()</li>

and saved. I then realized that this was incorrect for a markdown file!! So I hit Control-Z to undo this change...
I got a popup error message saying something about "[some error message that I didn't read], unable to apply undo operation" ...
Sadly, I closed the window without fully reading it - BAD move on my part!!

Anyway, I'm now sitting here looking at the file...
I can type new data into the file, but the "changed" flag doesn't seem to get set; the green bar on the tab for the file does not change to yellow,
and I cannot save the file... I also cannot undo anything that I type now...

Note: all other files that I have open (8 files in total) *can* still be edited, undo-ed, and saved, only readme.md is broken.

Sadly, I am *not* using the debug version of RJTE ...

I'll try to keep this open in my editor, in case there is anything else you wish me to look at.

Well, I just went to an html file, typed in the three lines of <li>some text</li> and then undo-ed them, and had no problem at all...

This is typical of the sporadic, strange, usually un-reproducible issues that I've been getting recently; they *roughly* began about the time 16.61 was released...
I wonder if something is going on with your performance optimizations that you did in that version??
Though apparently nobody but me is seeing any of this...
Maybe it is Windows 10-related??

I tried editing, undo/redo using some debug tools (to check for memory issues, overflow and range checking ...), but can't find anything wrong.

I think you have to do a specific action for this to happen. Anything you may have done before it happens could be very helpful. E.g. running a macro, selection and replace, code completion, some editing function you often use with a keyboard shortcut, multi cursor editing...