When I read the first point in the first post I get the impression that the problem is precisely that Insert Special Character inserts into the Replace field, not the CodeView.
The OP also mentions "couple crashing", but this is probably a problem that has been discussed several times (e.g.
here,
here,
here, and
here).
The notifications described relate most often to Clips, but also occur with Insert Special Characters.
There are a lot of reports about this in the Qt database and the problem likes to recur. In my case, I see this error frequently, but I know that it can be related to other applications that capture the clipboard, and the message itself does not discourage me from using Sigil
