"Is this a recognized problem? Yes, see Athanasius', above.
"Is it a problem at all? Yes, but not one that's apt to be resolved other than by careful choice among the alternate approaches.
"Does it look like it needs to be reported as a bug? No; see 1 above
Does this "mean that alterations with grouping should be avoided at all...?" Definitely not; sometimes the difference in speed is too small to make any difference; sometimes the clarity of one approach clearly outweighs any other issues; and sometimes other factors, like personal taste, can be allowed to determine. Just be sure to think carefully about which applies.
Re: alternation in regexes: to use or to avoid?