Cron is triggered several times instead of just once

[Mrasnika]

A little foreword:
I have a custom made plugin which uses the cron/schedule feature of WP. It has several "routines" in it, which you can call each 1hrs, 2hrs, 6hrs, 24hrs, etc. One of these "routines" inserts new posts when a condition is met.

The problem:
The cron task is called multiple times when it times has come. This results in inserting several identical posts. For example a routine is due to run each 6hrs, and insert a post reporting the number of comments that were submitted in the last 6hrs. This routine should produce only one post like that, while now it varies from 2 to 8. To investigate what the problem is I made the "routine" report the time of its execution and that's how I identified that wp-cron.php is called multiple times instead of just one (the period is 6hrs, and the format is date('Y-m-d-_His') + microtime(1)):

2008-01-21_062803.(1200925683.07)
2008-01-21_080824.(1200931704.85)
2008-01-21_080825.(1200931705.84)
2008-01-21_080848.(1200931728.36)
2008-01-21_080849.(1200931729.83)
2008-01-21_080850.(1200931730.19)
2008-01-21_140804.(1200953284.51)
2008-01-21_140806.(1200953286.05)
2008-01-21_140815.(1200953295.16)
2008-01-21_140816.(1200953296.72)
2008-01-21_140818.(1200953298.95)
2008-01-21_140818.(1200953298.98)
2008-01-21_140820.(1200953300.43)
2008-01-21_140821.(1200953301.45)
2008-01-21_140821.(1200953301.93)
2008-01-21_140822.(1200953302.1)
2008-01-21_140822.(1200953302.67)
2008-01-21_140822.(1200953302.7)
2008-01-21_140822.(1200953302.75)
2008-01-21_140822.(1200953302.81)
2008-01-21_140823.(1200953303.44)
2008-01-21_140823.(1200953303.52)
2008-01-21_140823.(1200953303.69)
2008-01-21_140823.(1200953303.89)
2008-01-21_140823.(1200953303.93)
2008-01-21_140824.(1200953304.53)
2008-01-21_140824.(1200953304.77)
2008-01-21_140826.(1200953306.06)
2008-01-21_140826.(1200953306.51)
2008-01-21_140826.(1200953306.63)
2008-01-21_200804.(1200974884.58)
2008-01-21_200809.(1200974889.21)
2008-01-21_200813.(1200974893.98)
2008-01-21_200814.(1200974894.07)
2008-01-21_200817.(1200974897.98)
2008-01-21_200818.(1200974898.87)
2008-01-21_200818.(1200974898.94)
2008-01-21_200818.(1200974898.96)
2008-01-21_200819.(1200974899.15)
2008-01-21_200819.(1200974899.22)
2008-01-21_200820.(1200974900.53)
2008-01-21_200820.(1200974900.55)
2008-01-21_200821.(1200974901.34)
2008-01-21_200821.(1200974901.82)
2008-01-21_200821.(1200974901.9)
2008-01-21_200822.(1200974902.36)
2008-01-21_200823.(1200974903.17)

You can see how we have multiple "timestamps" recorded for each 6hrs, while there should be only one.

Note, that I checked my "cron" setting in wp_options table and it has no excess hooks, but just the ones I use.

Observations:
I am not 100% sure but my observations are that this started happening after upgrading to 2.3.2; I haven't encountered such issues before that.

[DD32]

Quick Check: Do you have the Object Cache enabled? (define('EBACLE_CACHE',true) in the wp-config file)

If so, Try disabling it:

define('DISABE_CACHE', true);

in #5199 that was brought up(options cache getting out of sync with database), and as of a result, The Object cache has been removed from 2.4/2.5(Yet others can still load a object cache file if they want to)

[DD32]

(define('EBACLE_CACHE',true)

Blah, Obviously:

(define('ENABLE_CACHE',true);

[jacobsantos]

The real issue is that the duplicate posts are being added. Checks should be made to ensure that the cron hasn't already ran.