Change of prim colour/opacity in attachments causes re-calculation of AVcentre point?

Been playing with simple glasses attachment. The glass prims have a script in them which adjusts the colour and transparency of prim faces at regular, short intervals.

the unexpected side-effect is, this adjustment of colour/opacity parameters (which doesn't even touch the overall size of attachment nor the size of prims in question) causes the whole AV bounce slightly up and down, as apparently the centre point of AV keeps shifting up and down by ~1-2 cm at each update... needless to say, it can look rather silly. As soon as updates to prim colour/opacity stops, the bouncing ceases.

Just puzzled what gives, mainly, as it really makes very little sense o.O;

I bug-reported a similar bug long ago in SL 1.7 (I think). It hasn't yet been resolved. In my case, a simple llLinkedMessage between two prims in an attachment causes jitter in the AV position, resulting in the annoying "hiccup" effect.

It seems to be a related problem.

Now, it gets really annoying when your objects needs to send lots of linked messages per second.