HTML is still available to the client after HTML is unchecked under Allowable Compose Views in client options.

Under Allowable Compose Views in client options, if HTML is unchecked, new messages sent by the client will still be able to send HTML content. Allowable Read Views must be checked and Disable HTML View must be unchecked to see the problem.

This is true whether you change client options at the PO or Domain level. 

Work around:  If you uncheck HTML at Allowable Read Views, or checkDisable HTML View, theHTMLoption on new messages will then be grayed out as expected but then both read and send views for HTML will be unavailable.

Steps To duplicate:
In ConsoleOne, Right click on the Domain or PO | GW utilities | client options | Environment | views
Under Allowable Compose Views, uncheck HTML (locked or unlocked is the same).

Now let this setting replicate to the PO, then open the client.  Create a new message then click on View and you will see that HTML is still available.  If you go to Tools | options | environment | views,  HTML is grayed out as it should be.

Tested with GW 7 sp1  ir1