Thank you for reporting this.
Looking in to the issue, this file is hosted on SourceForge, which requires several web server redirects before downloading the actual installer. I’ve checked into our tooling that builds the URL and size/hash checks on the files, and our tooling is not correctly following all of the server redirects and thus we are generating incorrect size and hash based on the HTML page that is issuing the file redirect, instead of on the file itself.
It may take us some time to correct this error. In the meantime if you need the Pidgin update immediately create a custom copy of the Fixlet and change the prefetch statement to
prefetch pidgin-2.14.10-offline.exe sha1:98ca1497c20dfd3e5f3d8432d4e0a79c24447776 size:35121600 https://sourceforge.net/projects/pidgin/files/Pidgin/2.14.10/pidgin-2.14.10-offline.exe sha256:3bb3186222a491aae4da1c87544da30dab405b0f7f974bba6fd60963ec6c73c6