Memcache writes can occasionally result in error, even when the server is up and running. Such cases could be:
- memcache is full, and automatic removal is disabled
- allowed memory is allocated, but there's no slab for the given data size.
Unfortunately this latter is very common, and bailing out in an error message is much more worse than simply not cacheing that certain data.
I propose, that such errors aren't reported when debug mode is off. So if performance degrades, and a developer checks the system in debug mode could notice the errors inmediately, but the production system is not affected.