Avoid trouble with filter and the_content in WordPress

One problem i just came across while working on my WordPress plugin that many might not know is the danger of making mistakes on filter and the_content action hook. The importance of 'the_content' action hook and where this particular small sentence will affect your overall WordPress and caused it to malfunction if WordPress plugin developer used it carelessly (scary stuff). In this article, i will show you some of the mistake i made and what are the consequences in screen shot to inform WordPress plugin developers what will happen to WordPress when this two is being used wrongly.

What is 'the_content and filter?

In case you don't know what is filter and the_content action hook, filter is used in WordPress to filter the data between WordPress and its database. Short to say, you can manipulate the data retrieved from WordPress database before it shows out. The 'the_content' action hook is used to tell WordPress to print the content of the post, short to say, i am trying to manipulate the data from WordPress before displaying out to the end-user.

Problem

i have a test site which use to debug and test my plugin in a test environment before implementing it on the LIVE site. Everything goes well on the TEST since there is only one plugin but problem came when there are more than one plugin which hell can happen, not only deal to naming or method contradiction but some other unknown problem can occurred. One of the very rarely unforeseen problem is the filter and 'the_content' action hook problem. By the way, I am using WordPress v2.8 for testing.

Consequences

Many might not know what will 'the_content' affect the internal and external of WordPress (Many might aware of the external consequences but not the internal ones). Let's take a look at one of my plugin tester site (http://1sitedaily.com) who reported these problems to me. In the post page, she was typing the post and this particular red thing came out of no where!
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