Some thoughts trying to have an overview of what happens.....
Posting & Locales
1) In good working original Osclass new ads are posted using the active locale.
2) In case someone changes language locale and starts editing his existing ad posted using another language locale when saving the edited ad is saved again using the new locale. In this case the ad is being duplicated and having differences where the owner probably doesn't know about!
3) Search is checking locale mainly when doing a text search
4) In case you simply press search without criteria the system shows ALL ads independant of locales
SO, my thought is that posting and editing of ads should always stick to the locale which was used when posting the ad to prevent the creation of duplicates and creating two different ad versions in two different locales!!
IMO this could be considered a bug or a feature with nasty side effects.
Next, to ignore the locales in text search (and maybe other criteria using locale) we need to simply take it out of the search query. This could be an Admin option and/or a core change OR this might be achieved with the search changes done by teseo using functions.php.
The latter was causing me issues BUT I also had an issue in my theme I wasn't aware of when posting new ads. One locale function being used in my header prevented it to work again in the body of the page causing my newly posted ads to be posted without the locale in the table! Causing my system to have ads with 1 locale, ad duplicates with different locale and different ad properties and ads without a locale.
As for the latter, I was able to fix my theme issue so my new ads are posted the correct way again and I will test the last solution again teseo created to see if that makes any difference as for working or not working 100%.
But most of all I want the edit of ads not create duplicates..... I am not sure if this should be considered a bug and I hope _Conejo is reading along and can shed a light on this.
All other thoughts very welcome here!