Thanks again. I'm running it on a couple of servers and haven't seen it trigger at all yet. I'll keep watching.
I think it's a case of, no news is good news.
My CLAM client hasn't logged any backward leaps for about 36 hours.
I got one:
2015-07-12 11:11:49 receive version message: version 60014, blocks=549117, us=, them=0.0.0.0:31174, peer=36.75.220.2:54944
2015-07-12 11:13:45 peer 36.75.220.2:54944: leap backwards in height request, from max 549812 to current 275001. penalty=1/100
2015-07-12 11:13:45 peer 36.75.220.2:54944: leap backwards in height request, from max 549812 to current 276001. penalty=2/100
2015-07-12 11:13:48 peer 36.75.220.2:54944: leap backwards in height request, from max 549812 to current 277001. penalty=3/100
2015-07-12 11:14:02 peer 36.75.220.2:54944: leap backwards in height request, from max 549812 to current 278001. penalty=4/100
2015-07-12 11:14:07 peer 36.75.220.2:54944: leap backwards in height request, from max 549812 to current 279001. penalty=5/100
2015-07-12 11:14:11 peer 36.75.220.2:54944: leap backwards in height request, from max 549813 to current 280001. penalty=6/100
2015-07-12 11:14:13 peer 36.75.220.2:54944: leap backwards in height request, from max 549818 to current 281001. penalty=7/100
2015-07-12 11:14:15 peer 36.75.220.2:54944: leap backwards in height request, from max 549823 to current 282001. penalty=8/100
2015-07-12 11:14:20 peer 36.75.220.2:54944: leap backwards in height request, from max 549833 to current 283001. penalty=9/100
2015-07-12 11:14:22 peer 36.75.220.2:54944: leap backwards in height request, from max 549839 to current 284001. penalty=10/100
2015-07-12 11:14:35 peer 36.75.220.2:54944: leap backwards in height request, from max 550015 to current 285001. penalty=11/100
2015-07-12 11:15:03 peer 36.75.220.2:54944: leap backwards in height request, from max 550407 to current 286001. penalty=12/100
2015-07-12 11:16:11 peer 36.75.220.2:54944: leap backwards in height request, from max 550576 to current 287001. penalty=13/100
2015-07-12 11:18:12 peer 36.75.220.2:54944: leap backwards in height request, from max 550582 to current 288001. penalty=14/100
2015-07-12 11:18:13 peer 36.75.220.2:54944: leap backwards in height request, from max 551047 to current 289001. penalty=15/100
There's no other mention of that peer in the log, so I don't know what happened to it, but that was a while ago now.
Do we have any understanding of why this happens, or ideas about how to prevent the next release from being similarly misbehaved when it is an old version some time in the future?