Google Webmaster Tools shows problems with duplicate title tags under Optimization -> HTML Improvements, for example:
ราคาแอร์ Mitsubishi Electric Mr. Slim PC Series PC-3KAKLT (220V) 30000 BTU
> /แอร์-ราคา/mitsubishi-mr-slim-pc3kaklt-30000-btu.html
> /แอร์-ราคา/mitsubishi-mr-slim-pc3kaklt-30000-btu.html?category_id=96
These two pages have exactly the same content, a rel-canonical tag is set, and they are (no longer) linked to internally. Additionally, we used the Configuration -> URL Parameters setting, to set this parameter to No: Doesn't affect page content about one month ago.
However, Google is still showing these HTML improvements (and rankings dropped dramatically).
What else can we do here?