Please find attached some tests with invalid rule keywords combinations (bad "grammar") that should not be loaded by the engine, nevertheless they are getting loaded.
modifiers and rule keywords - distance,within, depth, offset...
Snort corrected some of the issues they had - ""Improved error checking for invalid combinations of "depth", "offset", "distance", and "within" modifiers in rules. Rules that mix relative and non-relative options on the same content will now cause errors."" - http://blog.snort.org/2010/12/snort-2903-is-coming-soon.html
dated back in Dec 2010, some of them are still not addressed, I believe.
Please find a comparison of invalid rules and if they load or not. I have tested all the bad rules with Sur 1.0.4/1.0.5/git master, Snort 184.108.40.206/220.127.116.11/current beta, the results are in the spreadsheet attached.