Conditionals problem combining with "==" works but "!=" doesn't

[L2V]

I am working on some template modifications and have come across a problem on my 3.7.2 test board. I am trying to get something to show up in all areas of the forum except for a showthread page, blog page or social groups page.

Check out these following code samples and please tell me if I am doing something wrong...

<if condition="THIS_SCRIPT != 'showthread'">not showthread<br /></if>
<if condition="THIS_SCRIPT != 'blog'">not blog<br /></if>
<if condition="THIS_SCRIPT != 'group'">not group<br /></if>

Behaves correctly and as expected

<if condition="THIS_SCRIPT == 'index' OR THIS_SCRIPT == 'forumdisplay' OR THIS_SCRIPT == 'usercp' OR THIS_SCRIPT == 'private' OR THIS_SCRIPT == 'memberlist' OR THIS_SCRIPT == 'search' OR THIS_SCRIPT == 'faq'">if is script test<br /></if>

Behaves as expected. If the page is any of these scripts it

<if condition="THIS_SCRIPT != 'showthread' OR THIS_SCRIPT != 'blog' OR THIS_SCRIPT != 'group'">not conditionals combined<br /></if>

Doesn't work at all. The test text show up on every page.

Why? Is it supposed to behave this way? What am I doing wrong?