Recently I managed to merge 3 very large WP blogs into one. I did so by exporting 2 of the blogs as WordPress XML files and then imported both of those into the 3rd blog. While there were a number of technical issues faced with the merger of 100s of thousands of comments and 30k+ posts, the merger seemed to go fairly well. The sites that were merged had hundreds of keywords.
The one problem I noticed immediately seems to be related to the internal WP rewrite process.
If I create a WP page called "My Page" which has a page slug of "my-page" and try to load that in a browser http://www.mysite.com/my-page, I will get an internal 500 error as seen through Firefox/Live HTTP headers. The headers include some from WP plugins such as W3 Total Cache so I know its hitting WP. There's nothing in the error logs so I know its not a server issue.
For the most part, the site works flawlessly. Even with turning off all plugins, the error is reproducible. There has been no problems with hundreds of posts that were added after the merger. Additionally, the problem appears to be related to tags that may have been imported. Assuming "My Page" was a tag with the tag slug of "my-page".
Is there a way to see how WP is doing the internal rewrite or to get a list of its internal rewrite rules? Related to this, is there a way to have WP rebuild its internal rewrite rules?