I thought I actually replied to this comment, I came back to let you know that I've worked out what the cause is (However, not on how to fix it)
Basically my script is going through folders and pulling out any image with "Preview" in the name - and is then applying the image to a button to be used for calling a function.
Anyway, decided to take another dig at finding out the cause - and I've noticed this:
Once the amount of buttons I have, with an image attached goes over 24 - I get this strange memory leak above, where reloading the script increases the memory used by maya. I've tried the technique above amongst other things - but no matter what Ive tried, nothing works.
Upon loading a script with more than 24 buttons increases memory usage significantly right off that bat. This is a shame, since I need to load many at the same time.