I read that some versions of IE6 have known issues with gzip compression, but I have found little explanation as to what these issues are. What are the known issues with gzip compression and IE6?
The problem is described in this answer.
If you are using Apache there is information at the Ultimate IE6 > Cheatsheet: How To Fix 25+ Internet Explorer 6 Bugs on how to work around it:
Some versions of IE6 prior to the XP SP2 update may have trouble with files that have been served using GZip compression. Fortunately, Seb Duggan found a IE6 GZip bug solution using ISAPI_Rewrite for Apache.
Seb's solution is to place the following code in the httpd.conf file in the ISAPI_Rewrite installation directory:
RewriteEngine on
RewriteCond %{HTTP:User-Agent} MSIE\ [56]
RewriteCond %{HTTP:User-Agent} !SV1
RewriteCond %{REQUEST_URI} \.(css|js)$
RewriteHeader Accept-Encoding: .* $1