[NiteWave]

Its seems that you can set apc.shm_size upto 249M and it works fine, as soon as you go over 250 then the locales stop working.

this suggested me a default setting for lsphp5 external app:

lsws admin console->Server->External App->lsphp5->
Memory Soft Limit (bytes):250M
Memory Hard Limit (bytes):300M

can you increase the soft/hard limit to 300M/350M and see if working for apc.shm_size = 256M ?