Hello
I compiled geofabrik.de Ireland OSM data with mkgmap (I made my tests with source code downloaded 2010/12/17) and the sea is generated only for one tile with "generate-sea=multipolygon,close-gaps=1000"but works well with "generate-sea=multipolygon,extend-sea-sectors,close-gaps=1000" ! With mkgmap version from august, it works well. Did you change an option for sea generation ?
There have been many changes, I'll let others answer this particular question though.
I also found two small problems with mkgmap's options : Option -version does not display a number but "svn". This is the same with old version (since 156x, I think)
If you build from subversion, then yes the version is displayed as "svn" as you could be building any kind of modified version of the code and getting the version would require an ant extension. But if you want to set up a build procedure that includes the version number all you have to do is arrange that there is a file called "version.properties" in the "resources" directory that contains the line: svn.version: 1733 where 1733 is the version number. You can have any string it doesn't have to be just numeric.
While I noticed you changed some options name, I found a annoying change : when mkgmap meets an option which is not needed for compilation phase, it stops with an error message like "invalid option". This happens only with "product-version" option.
Any option that is not documented in the options help file is treated as "invalid". You are right that "product-version" is used but not documented, so I shall add it. ..Steve