Code completion for xhtml files does not use TLDs. JBoss Tools uses its own XMLs which are generated from TLDs. We need it to provide some aditional info for Code Assist. JBoss Tools recognize tags of seam 1.2 and 2.0.0. It looks at tld within project and use XML for proper version of tld.
I guess you use Seam 2.0.1. But that tld has the same version (2.0) as Seam 2.0.0 TLD. So when you get proposals in XHTML in project with Seam 2.0.1 you get proposals from our XML for Seam 2.0.0 TLD.
JSP Editor use real TLDs for Code Complition and it doesn't have such problems.
It's a problem and I think we should improve our code assist for XHTML.
Here is a workaround:
You can edit /eclipse/plugins/org.jboss.tools.common.kb_\schemas\tld\JBossSeam2_0.xml
to provide correct proposals for Seam 2.0.1
If the XML schemas for code completion are generated, perhaps a tool for generating schemas for custom taglibs from TLDs would be useful somewhere in JBoss Tools?