Weird behavior when querying ItemMatrix endpoint

in Development
I'm querying the ItemMatrix endpoint to search for products. If I query directly using the following:
?description=%7E%2C%25fergie%25
I get the expected results. However, if i try to use an or block:
?or=description%3d%7E%2C%25fergie%25
it fails to find the expected results.
Another weird piece is that if I add a wildcard character between the f and the e in the query string, it finds the expected results.
?or=description%3d%7E%2C%25f%25ergie%25
It also works if I leave the f off of the the search term all together:
?or=description%3d%7E%2C%25ergie%25
Is the api decoding %25f as something and causing this to fail? Any other thoughts?