Uh, I think I've made a SNAFU in DR... Perhaps it's a bug.
Either way, unless there's a simple fix for a SNAFU, it looks like a clean deinstall/reinstall of DR to fix what might be a bug.
I changed an entity, to test, to one of the entity classes that is a damage def - at the bottom of the list - "damage_triggerhurt_25".
Doing this removed the brush from appearing in TDM. No damage.
OK, np, I kinda knew these didn't work but thought I'd try them anyway.
Changing back to "trigger_hurt" - it appears and causes damage to the player as it did before.
So decided to try changing the entity to "atdm:damage_moveable" to see if it worked or not.
Doing this also removed the brush from appearing in TDM. No damage.
After this - if I create a new brush, it is impossible to change it from worldspawn to ANY entity class at all.
However - I am able to change the entity class of any existing object in DR.
Selecting the brush, clicking the classname in the entity info panel under camera view and then using the "choose entity class" button to bring up the menu, I get the list - but selecting any class and then clicking "add" does nothing.
Even if I select the brush and then type in the name of the entity, eg "trigger_multiple", under classname - it will not store any change, clicking the tick or pressing enter on the keyboard.
This persists after (both software and computer) restart, in other maps and in any new map I create.
I am able to change the entity class of any existing object by either of these "usual" methods otherwise.
The only way I am able to change a new worldspawn brush into an entity is to select the brush and then right-click and select, "create entity" to bring up the same list from which to select, eg "trigger_mulitple" as I would by clicking the button in the entity info panel.
Once the entity is created this way - it is then possible to change it using the entity info panel method or by typing in the entity class into the classname box, as usual.
(it is often faster to type [/paste] "func_static" into the classname box than navigate to "func_static" by creating an entity from worldspawn using the "choose entity class" button or right-click "create entity")
Furthermore, it appears as if some filters have been activated by choosing these entity classes - meaning that it looks as if deselecting a clip or nodraw texture is deleting the worldspawn brush / func_static.
The filters it did activate are "clip textures", "func_static entities" (even though they are evidently displayed with any other texture but clip or nodraw...), "nodraw", "visportals" and "world geometry".
These are filters that I have had selected several instances of DR ago, but since have deactivated all filters... The recent files are correctly displayed.
Once again deactivating all the filters - it is still impossible to create an entity by any other method than right-clicking it, instead of simply typing in the worldclass box or accessing the entity class directory through the entity info panel button.