ON the Toaster Project page, the hover-help for the edit box with place-holder "type the recipe you want to build" says "you can also specify a task by appending a semicolon and a task name to the recipe name, like so: busybox:clean" The example uses a colon(:) not a semicolon(;).
Patch sent to Toaster mailing list https://lists.yoctoproject.org/pipermail/toaster/2016-March/004321.html
Fixed in bitbake 691419e23a94a94129b177e71d2c728b12689139.
Verified.