Entry with link takes 30 second to save

I have some performance problem while using MT 4.34.

Env: Ubuntu 10.04, Apache 2, run MT in CGI mode
Setting: no plugin, only save article in draft
No spam entry detect. No ping out.

I use performance log to get the performance data.
First I post an entry without any content. It takes 0.58 seconds.
You can see the total time in the end of the line.

[Sun Oct 17 15:56:26 2010] othree-server pt-times: pid=23706, uri=[/mt/mt.cgi?authored_on_time=15%3A55%3A54&magic_token=tO2CjFKsIppYC7nl2o8Mh7reVTHvxwfJQLNYgEKi&excerpt=&status=1&_ignore_tags=&keywords=&basename_manual=0&convert_breaks=0&return_args=__mode%3Dview%26_type%3Dentry%26blog_id%3D1%26id%3D643&__mode=save_entry&text=&text_more=&allow_pings=1&include_asset_ids=&blog_id=1&id=643&to_ping_urls=&category_ids=&itemset_action_input=&text_height=470&_type=entry&allow_comments=1&tags=&_text_=&basename_old=test&action_name=&title=test&authored_on_date=2010-10-17], mem_start=7484, mem_end=24092, Total=0.58203

Then I edit the entry content. Just add one single link.

<a href="http://google.com"></a>

The time it spend to save the entry becomes 31 seconds

[Sun Oct 17 15:57:03 2010] othree-server pt-times: pid=23720, uri=[/mt/mt.cgi?authored_on_time=15%3A55%3A54&magic_token=tO2CjFKsIppYC7nl2o8Mh7reVTHvxwfJQLNYgEKi&excerpt=&status=1&_ignore_tags=&keywords=&basename_manual=0&convert_breaks=0&return_args=__mode%3Dview%26_type%3Dentry%26blog_id%3D1%26id%3D643&__mode=save_entry&text=%3Ca%20href%3D%22http%3A%2F%2Fgoogle.com%22%3E%3C%2Fa%3E&text_more=&allow_pings=1&include_asset_ids=&blog_id=1&id=643&to_ping_urls=&category_ids=&itemset_action_input=&text_height=470&_type=entry&allow_comments=1&tags=&_text_=%3Ca%20href%3D%22http%3A%2F%2Fgoogle.com%22%3E%3C%2Fa%3E&basename_old=test&action_name=&title=test&authored_on_date=2010-10-17], mem_start=7488, mem_end=27460, Total=31.13776

I have done lots of test. See slow query. Use background job. Try fastcgi. But none of them fix this problem.
Since 30 seconds feels like a timeout setting for some web server. It makes me feel like that MT is doing a http request and get timeout during the save process. But I can't find any setting can avoid this behavior.

Does anyone know what is wrong with my setting ?
Or this is a MT bug ?