Clearly for reasons of ??? SHP Builder won't agree to do resize to anything larger than said dimensions and percentage tools default max at 500x 500...

say you load an 1024x1024 shp image in and go resize down by percentage say 25% (by picking 75 in editor), the size field will go to 500x500 which is of course incorrect, curiously enough works fine on lower sizes and inputting own wanted size also fails and shp builder forcibly inserts 500x500 unless you specify that or lower yourself.

Also canvas tool when using larger resolutions shows the area border incorrectly preview wise indicating area to be removed while it does work fine in removal the preview is wrong and sadly it also limits to doing like -100 -100 or something multiple times in row as it can get fooled into thinking there is no room left to remove using larger values while there would be.