I have had various issues with either of those keyservers. The keys.gnupg.com site in particular does not seem to like searches unless they are exact. The mit keyserver seems to require a longer string when doing a search, so they may have a length requirement. Unfortunately, while the basics of PGP are the same, there is no telling how those openPGP keyservers are configured or what they might require as input.
I have only managed to get a response from the keys.gnupg.net when I send a perfect match. The keyserver might not be able to process certain requests correctly, such as the "name" + "contains" searches. Again, I have no clue how it might be set up, but that was my experience in testing.
In both cases, it seems like the search doesn't actually resolve on some attempts, so maybe the PGPtray is still waiting for a response, and never receives one. That might eventually cause the PGPtray to crash, but I don't recall any bugs or cases related to that.