I have noticed that the 'not finding what you're looking for make a purchase suggestion' box doesn't appear consistently. I have to admit I don't have much information on what could be causing this but I wanted to report the issue. What I've seen is that on all opacs I've tested the link shows at the bottom of some searches and not others - and it shows on some 'no results found' pages and not others. This is all on one system - not that it works on some and not others - that it's inconsistent within one system depending on what you search for and where you search from. This is with CCSR on Koha 3.12.4 and master in Firefox on Mac & Windows.
I found it! See here: http://screencast.com/t/akXrkZkuF I think it has to do with the 'did you mean' interfering with the 'would you like to make a suggestion' box. If you don't have 'did you mean' enabled then this still happens.
I can't reproduce this bug in master using the bootstrap theme.