Mail notifications delayed long past receipt of the email

REPRODUCIBILITY (% or how often): randomly
BUILD ID = OS VERSION (Settings > About product): 4.0.1.48
HARDWARE (XA2, Xperia 10…): XA2
UI LANGUAGE:English
REGRESSION: (compared to previous public release: Yes, No, ?): Yes

DESCRIPTION:

Receiving a new email to either an Exchange account or an imap account (it doesn’t seem to matter), the email is received and appears both in the mail app’s inbox for that account and on the home screen (the one with the weather, calendar entries, twitter feed, etc) but the notification banner and alert tone for that email may not appear until sometime later (I’ve had notification banners and alert tones up to an hour after the email has been received).

At other times the banner notification and alert come immediately the email is received.

PRECONDITIONS:

Receive an email.

STEPS TO REPRODUCE:

  1. receive an email
  2. email appears in inbox and on home screen
  3. banner and alert tone happen immediately or some variable time afterwards

EXPECTED RESULT:

Banner and alert tone should always occur when the email is received.

ACTUAL RESULT:

banner and alert tone happen immediately or some variable time afterwards in a completely random manner

ADDITIONAL INFORMATION:

(Please ALWAYS attach relevant data such as logs, screenshots, etc…)