2
It's a guess, but I suppose the new sanitising of DB queries and form elements in 2.0.18 could cause a form to fail if the form submitted an integer value as text?
The sanitisation seems to be the only significant code change if the 2.0.18 release notes are to be believed.
Security improvements are great, but it would be useful if the core devs could publish some info on how to check a module for incompatibilities. It may be a very simple fix.
A thread is for life. Not just for Christmas.