Verified with 2.6.0
Using a zone JS invocation with block=1 in 2.6.0 will work. However using a 2.0-based invocation for the exact same zone & adserver will not result in blocked banners.
For example, using firebug I see that one invocation tag selects and outputs bannerID 99. Another invocation tag later on selects bannerID 33 but outputs bannerID 99
Can the issue be reproduced in IE?