For some edits (I am almost sure that it is only edits are made from the mobile version, i.e. http://<lang_code>.m.wikipedia.org/), the abusefilter variable "new_wikitext" contains only the text of the edited section, while "old_wikitext" contains the full text of the article. As a consequence, there are currently many false positives for filters that trigger on large deletions.
For exemple, the following entry in the log of http://en.wikipedia.org/wiki/Special:AbuseFilter/30 ("Large deletion from article by new editors") shows a huge deletion:
However, there is no deletion in the actual diff (which is incorrectly tagged with "Tag: blanking"):