drupal loses track of a library (leaflet), randomly I have an strange problem with a library (leaflet). 

I have some maps, and it works fine, but randomly (as far as I have been able to detect) drupal is unable to find leaflet.js and leaflet.css (it is allways located in sites/all/libraries/leaflet , as indicated in leaflet drupal module website).In fact I can see in Firebug that Drupal is not even trying to get the library (I get no server error message saying it cannot find the files or similar)

When this 'error' happens, I have to do strange things like moving the leaflet.js file to another folder or change the name and then, after drupal fails and I rename the file again, MAYBE drupal is able to find it again. Sometimes it seems like flushing cashes helps but not allways...I know it sound dummy but it only happens with this libarry and it seems completely random. Hours wasted trying to set up again...

The folder is 755 in permissions. Have tested in a different PC and the same problem! changing browser or clearing its cache doesn't help neither.

thanks in advance
How do you see that drupal does not find that files? Is it correct that you just get 404 for that files in browser? Try to load these files in browser window like http://yourdomain.com/sites/all/libraries/leaflet/leaflet.js. If it's not loaded, it's your server issue, rather than drupal one.