I've used several programs, all on mint, and created usb's with all of them, with persistence, for the life of me, can't remember which ones but . . . . I've used unetbootin, a lot, usb disc creator, image writer, YUMI and multiboot - I'm going to guess at unetbootin and usb disc creator as the successful prog's - one odd thing I've noticed on occasion is a failure to write on one program, only for another to complete it. Why I've no idea, but sometimes the format/fat32/ntfs/ext2 etc has seemed to make a difference and wiping all partitions off the stick/drive and reformatting has done it for me. Don't see why it could be mint as such at fault as it's based on Ubuntu..... ?
Lenovo ThinkPad T61 LM14 & 15 (different HDDs) Intel T7500/2.2GHz/Cinammon 1.6/1.8 Intel GM965. Toshiba Satellite M70: Dual boot Zorin OS & Elementary.Desktop:LM13/15 Geforce 9500 GT, Athlon 7750 Dual-Core 2700mhz,3gb RAM.Linux Registered #562462