Front page refuses to get cached

I have a problem with the page cache where the front page (http://domain.com/) refuses to get cached, while the same page loaded explicitly (http://domain.com/my_site_frontpage) caches fine. I've confirmed this by looking at the X-Drupal-Cache header.

If i change the page cache to use database caching ($conf['cache_class_cache_page'] = 'DrupalDatabaseCache';) the problem goes away. This is an acceptable workaround for me, but it would still be nice to figure out why this happens.

Ubuntu 10.04.4 LTS

PHP 5.3.2-1ubuntu4.15
APC 3.1.3p1

PECL memcache 2.2.6 stable

Config:
memcache.allow_failover	1
memcache.chunk_size	8192
memcache.default_port	11211
memcache.default_timeout_ms	1000
memcache.hash_function	crc32
memcache.hash_strategy	consistent
memcache.max_failover_attempts	20

Drupal 7.14
Memcache 7.x-1.0