Yes, this is definitely a mod-security / OWASP issue.
I use a helpful server-provider frim, who've bypassed dozens - yes dozens - of 'rules' which trap DW posts.
The 'rules' keep changing, and new ones are popping up all the time, I have to contact the server provider, with times and IP numbers, and they track-down and byapss that particular rule.
If you don't have a very freindly server-provider, this can mean quite big trouble for some DW installations.
The only other way around I've found (which I have to use quite a bit) is to FTP download the relevant .txt file for the page you're working on, edit it, and FTP it back.