Updated: Comment #N
DrupalKernel contains code that attempts to support multiple webservers for the same site, by detecting module changes and rebuilding the container if it changed.
That code a) only supports a very limited set of possible situations where this could happen (like pushing new code with different services or adding a language) and b) Affects performance for all the sites that don't use multiple webservers for no reason.
We have ideas to solve this problem in a better way, like comparing a flag in the database and one in a file and rebuild on mismatch. This can be done outside of core, optionally, to avoid the overhead for sites that don't need it.
User interface changes
PASSED: [[SimpleTest]]: [PHP 5.4 MySQL] 71,653 pass(es). View
PASSED: [[SimpleTest]]: [PHP 5.4 MySQL] 71,212 pass(es). View