There are many speculations as to why BTA have or do not have bubble tips. For example, some claim that the anemones form bubble tips when there isn't enough flow, they are not being fed well, or water parameters are off. Others claim it is from shock, i.e - water changes, new tank, etc. Personally, I can't say if any of that is true. I know my RBTA had bubble tips when I first got it. Once it was established it formed nice, long tentacles. When it split it also formed bubbles. IME, it seems perfect water quality equals no bubbles.
Here is what I have researched: "Loss of "bubbles" has been speculated to be due to insufficient light, current, feeding, presence of host fish/es, reaction to competitive influence/s... At this moment "the jury is still out" on this issue. The degree of bubbled-ended-ness does seem to be positively correlated with more current, less feeding, the presence of symbionts and other Cnidarians though. The bubbliness is evidently not a matter of life/death, good/bad... as specimens of both can/do well, and they do change back/forth at times from no apparent provocation." -
Shimek, Ronald L. 2003