Search and filters with contains

When I select a specific string field “Search Tax” the “Contains” option is missing.  When I select a different string field “Search Name” the “Contains” appears.  If I then select the first String Field “Search Tax” and save the “Contains” disappears.

https://drive.google.com/file/d/0B409lhd9sYDcX3p2RjladDRlTXM/edit

Hey Bill, 

Is Search Tax a formula field? If memory recalls, formula fields are not searchable since they are calculated at runtime. 

Regards,
Irvin

I have been using formula fields to create a field of concatenated data for my search field. Then when I do my filter I can look in just one field. I have built many searches in this manner. As can been seen in the following picture.

I noticed my first video did not play.  Here it is again.  I think it may have something to do with the length of the concatenated field.  I split the field into smaller fields and then query both fields and it works.  Is there limit on the length of field being searched?
https://drive.google.com/file/d/0Bw_R0LtXRtg3eHFLaURCYkVwcHM/view?usp=sharing

Bill - what is the field type of the formula field.  The contains operator only works on certain field types. 

It is a text formula field.  Everything seems to work fine if the concatenated field does not get to long.