Keyword filter not showing as a drop down in "Execute"

[seegupt]

In my Test Project, I created a keyword "Regression" and assigned this keyword to few test cases.

Now when I go to the Execute for the Test Plan of this Test Project, I try to setup the filter where I do not want to select any particular keyword.
i.e.
I am trying to execute all the test cases irrespective of their attachment to a keyword but Keyword field does not show as a drop down menu where I can select either "any" or "regression" rather filter shows only one value for keyword and that is "regression" and does not allow me to de-select this value.

So the only test cases that it allows me to execute is the ones that are attached to keyword "regression". Is this a bug that I am not able to see keyword field as a drop down or this is some configuration issue. Please clarify. I am using TestLink 1.8.5.

[fman]

1. http://www.teamst.org/forum/viewtopic.php?f=9&t=1328
2. 1.8.x is not longer maintained => migrate to 1.9.1