When connecting to a minecraft server that uses a texturepack and texture packs are enabled in the server list, an error is thrown and it disconnects you from that server. If in the server list it is set to 'Prompt' it will crash the minecraft client. See the attachment image. Error log: http://pastebin.com/99D7Zg6r
Dupe of MC-81082
In addition, Windows 10 is in public beta, and as such is currently not supported.