Could it be possible that OziExplorer is storing tiles into some local cache? Anyway, because the data obviously is all right in the OSM database and slippy map then the problem must be on Ozi side. Ozi users have a mailing list also.
The problem was that OziExplorer caches the OSM / internet maps data.
Short cut solution: throw the Ozi’s “systeme files\Internet Maps Cache*” files away. A fresh set will be downloaded after restart.
Structural solution: Ozi will be adapted by … having an option to ignore the cache and download fresh tiles.