I noticed, that the T3 Framework (2.7.3) has a problem with the head-section in the error.php template.
It's pretty mixed up html-code what get's generated. The <head> section is empty. What should be in the <head> section from the error.php is generated somewhere in the <body> section and as template still some of the html overrides (depending on what component etc.) is used.
As example create an html override for the article component in the t3_bs3_blank template. Create on purpuse an php error in your override template. Look now on the generated HTML Code....
Any ideas how to correct this?