If multicast handling is broken on your client, it might not be receiving certain broadcast packets (in 802.11, broadcast is a subset of multicast) that are fundamental to low-level network operation. If that doesn't solve the problem, then it's probably not a power save handling bug, but for now, continue to operate with 802.11 power save disabled, in case the bug is triggered by a combination of things. This may be called something like 'max performance mode' rather than 'power save off'.
To see if it's an 802.11 power save handling problem, disable 802.11 power save mode in the settings for your wireless driver. These kinds of partial connectivity problems on Wi-Fi usually come down to buggy implementations of 802.11 multicast handling, or broken implementations of 802.11 power save handling.
