cache->put does not behave as expected when $acm_type='apc'

I'm using an extension of my own, in which I use the @cache object.
When I use memcache as ACM. It behaves as expected : cache->put with a ttl of 300 makes entry disappears after 300 second : subsequent cache->get in an other php session returns entries
When I use apc, and cache->put does not behave as expected : nothing is stored in apc user cache. Subsequent get returns false