1) create a new subscription
2) search for a vendor who has spaces in their name
3) choose it, and note that when its name is put into the field, it has %20 where spaces should be.
Created attachment 2682 [details] [review]
This bug is mentioned in:
Bug 5294 - Unescape vendor name when pushing back http://lists.koha-community.org/pipermail/koha-patches/2010-October/012656.html
Pushed, please test