What ester(s) are involved? Usually, short esters can cause this issue. Crystallization in the muscle occurs from the short ester. If the mix is of high concentration as mentioned above, plus contains short esters, you more than likely will be in for pain.
The short estered culprit will "fall" out of solution INSIDE of your muscle. Think of it like this, injecting table salt into your muscle. Make sense?
BA is not always the culprit, infact most labs tend to keep the BA% on the low end and bump the BB%. Still, the problem is usually the hormone. As someone said, short esters hurt more than long estered hormones, however long esters can hurt as well if they are dosed high enough.