OK, guys....let's try to find an alternate word to 'spastic' as that pertains specifically to those with cerebral palsy, which I am certain is not the case with a bootskin progress bar.
The word is demonised by degrading reference, so much so that 'The Spastic Society' which helps care for those afflicted has been forced to dissociate itself from the connotation and rename to 'Scope'.
Just some 'facts' to show how educational the Net really is. My personal issue is that my Wife has been a Speech Pathologist with the Society for approx 22 years so let's just say that it's equivalent to referring to an 'African American' as a 'nigger' and leave it at that.
The word you want is 'spasmodic' or 'erratic'...