By "stick" do you mean you hit spin and there's a lag? or try to stop them with the same delay? I often like to "speed click" (for lack of a better term meaning: spin/stop spin/stop etc as fast as I can in an attempt to reach the feature- note: not for the timid) If this is what's meant by sticking, I have made some observations with this occurance:
1) It is limited to RTG as you mentioned
2) it is NOT your comp or connection speed due to:
a. opening another RTG site (more on which,see #6) produces fast responses
b. ping times to and from either fast or slow casinos are fairly equal
c. for whatever reason, it's the time
at the casino server that is delayed
3) Rogue casino groups are particularly prone to this anomaly while accredited casinos are far less afflicted- but not immune
4) Deleting cookies, remove/reinstall program has no impact on this delay
5) My win percentage
seems to decrease substantially and on sites where the reel speed is slow as well, it even seems worse (pal o chance exhibits this behavior quite often, for one) - this is subjective, though
6) I've rarely experienced this phenomena at CM endorsed RTG casinos.
*I haven't noticed any correlation to updates- But i'll be more aware and observant now
There are a couple more things I suspect but are totally without supporting experience, so those are on the shelf until I expand my trials- could be a long wait as i avoid the casinos that exhibit these symptoms.
So long as we're on the subject, another thing I've had happened is the apparently random occurence of the reels spinning at a regular pace when outta nowhere you'll get a rapid-fire turbo spin or two in the mix. I suspect it may have something to do with a software security measure and again this only happens at RTG. any thoughts on this, anyone?
Disclaimer......of course, on the other hand I could be full of chit and making connections that don't exist. Tough to get a true result when sampling one click at a time. I'll take whatever verbal abuse I may deserve on this one.

And if you meant something different by "sticking" then, sorry! nevermind!