Cannot reproduce based on your description.
Since you use Word, you must be on Windows. Which version? And which version of Word?
Next version question: Which version of Lazarus? Of FPC? 32bit or 64 bit?
If I understand correctly, the only copy operation goes from the IDE to Word? You copy a section of your source code? Just to make sure you do not make any intentional paste operation into the IDE? And within Word? You do only the only initial paste or any other copy/paste operations?
When I do a Ctrl+C with some highlighted text in the IDE, and paste it into word (with Ctrl+V), my clipboard viewer (
https://sourceforge.net/p/wp-laz/code/HEAD/tree/ClipboardExplorer/) shows me that the clipboard contains the formats
1 - CF_TEXT
7 - CF_OEMTEXT
13 - CF_UNICODETEXT
16 - CF_LOCALE
49991 - Application/X-Laz-SynEdit-Tagged
I would say: This is nothing special: When I copy some text into the clipboard from Notepad++ I get the same formats, except for the Lazarus specific 49991.
You say: "I clicked directly on my primary project (not the temp.lpr) and loaded it in the IDE". Does this mean that you double-click on the project.lpr (or .lpi) file in the Windows explorer? Maybe this is a difference because I cannot do this since I have so many parallel versions of Lazarus. Does the error also appear when you first open the IDE and then open the project in the "File" menu or the recently-used files menu?
Since you had closed all main project units in one of the previous steps, the project now opens will all forms closed. Same with you? Do you open any files here again? Or do you simply start compiling and notice the broken source code now?
Do you have any utility apps running which create a "Ctrl+V" on special occasions?