hi, just tried to fix some minor boundary problems in your country Slovakia and than i found:
dozend of boundaries exist as two exact identical areas - one with admin_level=9 and one with admin_level=10.
sorry, but that can’t be true.
https://www.openstreetmap.org/relation/2218547 and https://www.openstreetmap.org/relation/2218498
or
https://www.openstreetmap.org/relation/2218559 and https://www.openstreetmap.org/relation/2218491
and more and more.
Regards
walter
Those examples are in Slovakia, not Slovenia.
Wrong forum or wrong examples?
Btw, we also have similar cases in Slovenia where administrativne unit (upravna enota) consist of only one commune (obÄŤina).
sorry, wrong forum 
we have the same in germany: extreme example berlin - it’s City (al8), County (al6) and State (al4) so it got AL4 as the only one. And many big cities like Wiesbaden, Cologne, Franfurt, … are AL8 AND AL6, so they got AL6.
Austria did the same with vienna and other countries do the same.
An area should get the highest Admin level when there are more of them. Like the boundary-ways, which too get the highest level of all possible values.
Regards
walter
btw: AL6 is “higher” than AL8 - do not confuse with the numbers 6 and 8.
and: did you know this? https://osm.wno-edv-service.de/boundaries/idx21o.jsp?zoom=9&lat=46.15386&lon=14.98612&layers=0BT&selected=218657_1699148_541729_1703687_541718_541722_1703387_1703668_1703918_1703400_1703401_1699230_1703402
Scroll down the tree on the left side to see what’s going on
no problem, glad we cleared it up!
Let’s look at a specific example i remember from a few months ago:
http://www.openstreetmap.org/relation/4185354 - AL8 - Izola commune (obÄŤina)
http://www.openstreetmap.org/relation/4185354 - AL7 - Izola administrative unit (upravna enota) normally* containing exactly one or more communes
Both could be named the same, but I systematically named areas on AL7 with “upravna enota”, because that combination appears more commonly than “občina” prefix.
These are identical boundaries on different administrative levels.
As i understand you AL8 boudary should be deleted, and remaining AL7 boundary renamed more neutral (dropping “administrative unit”/“upravna enota” from the name). Renaming should then be done for all AL7 boundaries.
Is this rule specified in OSM wiki somewhere?
There are several more such cases in Slovenia, see Regions in Slovenia.
*There are exeptions, such as občina Ivančna gorica, which is split between Upravna Enota Litija and Upravna Enota Grosuplje. With no exact border defined (at least not until we import exact borders of individual settlements), making it even more fun. Also občina Pesnica is split between Upravna enota Maribor and Upravna enota Pesnica…
There’s still a lot to do… http://wiki.openstreetmap.org/wiki/WikiProject_Slovenia/Regije