IE9 only _sometimes_ ignores <base href>

Question

We are developing a site which makes heavy use of (which is typical for TYPO3 sites). The site is developed in a sub directory and will later be r

Answer 1

We found it: Internet Explorer does all sorts of funny things when the HTML file returned from the server contains a UTF-8 BOM. We still consider this a IE bug but at least we found a work around.

Background info: During initial page generation some PHP files where included which are not included for successive requests (because most generated content is cached now and these files do not need to be run). Some of such included PHP files included a UTF-8 BOM. Because the BOM comes before the opening PHP tag, it is streamed out to the output of PHP.

We figured it out by comparing outputs in fiddler and the file sizes differed by 3, 6 or 9 bytes when the error occured. Running a diff over the outputs showed the BOM header, comparing in most Windows editors didn't show it because these editors know about a BOM. So the problem was hidden. Thank you IE for 2.5 days of useless work!