OK, so my fears were true then.
Is there any way to get over this problem? For example, using Goba's suggestion to tag the date/time to the build?
Maybe a better solution is to keep the first two digits the same, then increment for every build. For example, we start at 4.5.0 with DRUPAL-4-5 as a tag, then have some fixes, then tag with DRUPAL-4-5-1 and make a build for 4.5.1 of that module/theme, then some more fixes, then 4.5.2, ...etc.
This means applying the same standard for core Drupal to the contrib modules and themes.
This way, when someone says he is using 4.5.0, then all other 4.5.0 would (hopefully) experience the same issue the first guy has.
Entirely wrong way! You are free to install any of the 4.5.x contrib modules to any 4.5.x core setup. This is not going to be cleaner to support, if we are not going out of the scope of these three digits. The contrib module version should have a component indicating the compatibility of the module with drupal (currently only this is included), and another component, which signifies its own progress, so support can be easier, and the need for updates can be detected... Your above suggestion mixes the two, and therefore it is not acceptable IMHO. Goba