Through various obscure manual manipulations it's possible to skip one or more rev numbers in an RCS history. RCS handles this fine, but RcsLite barfs on it.
Specifically the problem is when writing revs, the RcsLite module assumes a contiguous sequence.
This is a very rare corner case, and not urgent to fix as it can only arise where RCS histories are manually manipulated - it can't be broken in normal use.
-- CrawfordCurrie - 30 Sep 2011