I'm having the same problem with the form designer.
I customized a form, trying to remove the First Name and Last Name fields and add a bunch of text (maybe 2 paragraphs) to the form text, then change the colors, backgrounds, border, etc, and it saves changes inconsistently. When I created the form initially, it let me save the changes, but when I went back to edit the form, it won't let me make changes, and in fact added back in some of the default settings without asking me.
I asked my hosting company about ModSecurity, and they looked through the apache logs and said there were no modsecurity problems, but they did find other problems. I've copied the email they sent me below.
Any ideas? I really like this plugin, but I just want it to work consistently...
[Log file moderated. Please use the pastebin]