Getting "Specified argument was out of the range of valid values" error trying to modify code in (4238465)

While trying to modify some code in the editor, I get the following error message. I am not able to replicate this on demand, it happens periodically.

Here is a description of what I was doing when this happened once...
On previous edit I'd added a criteria to the where:
description LIKE '%dispatch%'
I copy pasted that query, edited a couple of other string values, then moused to the beginning of the word 'dispatch'. Got the error.
Saved the text file, went to another toad session that was already running. Opened the file. Went to that line, clicked. Got the error.
Closed Toad. Opened Toad.
Opened file. Used keyboard to navigate to that field. Didn't get the error.
Just now, I opened the file again. I went to that line, clicked in front of dispatch, was able to edit.
I then moused down to the pasted query at the bottom. Clicked in the last string criterion, now '%TIRE%'. Got the error. Hadn't tried to use the keyboard/select/make any change. Just a click.
Curious if it was a 'last value on page' thing or if it mattered if there were % signs in the values.
I moved an = 'CM' criterion to the bottom, saved, closed, reopened. Got the error clicking in 'CM'. Closed, reopened. Also still got the error in the no-longer-last string value with %TIRE%.
Did a few more rapid succession tests. Just seeming to crash on stuff in the last query on the page, but not with any consistent factor I can identify.

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Exception Information
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Exception: System.ArgumentOutOfRangeException
Message : Specified argument was out of the range of valid values.
Parameter name: index
Stack Trace:
at ActiproSoftware.SyntaxEditor.DocumentLineCollection.get_Item(Int32
index)
at
Que

WORKAROUND:
Turn off code completion by selecting Tools | Options | Editor-Code Completion and uncheck the ‘Auto List Members’ option.