As of r42471 [1], prop=revisions&rvprop=content will no longer throw an error when too many titles or revisions are specified, but will throw a warning and ignore the superfluous titles/revisions. The warning message is identical to the one issued when too many values are specified for the titles or revids parameter.
This change was made to fix bug 16074 [2], which occurred when a generator with gXXlimit=max (or any sufficiently high limit, really) was used to feed prop=revisions&rvprop=content, which would then throw an error because it was fed too many titles or revisions. However, the generator is not aware that prop=revisions threw away most of its results, and will set a query-continue as if this didn't happen. If this query-continue value is used by the client, a (potentially large) number of results will be skipped. When continuing such a request (i.e. one with a generator feeding prop=revisions&rvprop=content with a high or maximum limit), you have to set gXXlimit to a sufficiently low value first, so prop=revisions doesn't receive too many results and doesn't throw stuff away. The right number can be found in the text of the warning message, which is always something like "Too many values supplied for parameter 'titles': the limit is 50" (note that both 'titles' and the number 50 may vary).
Finally, it should be noted that this behavior can only occur with prop=revisions&rvprop=content and only when a generator is used to feed it. All other modules and all uses of prop=revisions not involving both rvprop=content and a generator are not affected.
Roan Kattouw (Catrope)
[1] http://www.mediawiki.org/wiki/Special:Code/MediaWiki/42471 [2] https://bugzilla.wikimedia.org/show_bug.cgi?id=16074