Dragging image - weird outcome...

Hi, I am relatively new to corona so bear with me and apologies if this is in the wrong forum. I’m ultimately trying to setup a drag & drop function for multiple ‘tiles’ on one scene. But to begin with (and to make sure I understand all of this correctly) I am just trying to get one tile moving around the screen.

So I browsed the interwebs for a while and found the solution below (among other similar solutions) and implemented this myself with my own object names etc.

It works great…but…unfortunately when I drag the object into the top right quadrant of the screen (on the simulator and a phone) the object gets stuck. It stops dragging as it hits any part of the top right quadrant of the screen, and I cannot re-select it to drag it back to the rest of the screen.

Any ideas as to why this is happening?? (my code is below)

local _H = display.contentHeight
local _W = display.contentWidth

local notesGroup = display.newGroup()

local tile1 = display.newImage (“graphics/image.PNG”)
tile1.x = _W/2
tile1.y = _H/2

function tile1:touch( event )
if event.phase == “began” then

self.markX = self.x – store x location of object
self.markY = self.y – store y location of object

elseif event.phase == “moved” then

local x = (event.x - event.xStart) + self.markX
local y = (event.y - event.yStart) + self.markY

self.x, self.y = x, y
end

return true

end

notesGroup:insert(tile1)

tile1:addEventListener(“touch”, tile1)

return notesGroup