Actually, no. In Magic when a permanent changes state it does not "enter play" as the new state. One of the oldest and clearest examples is Mishra's Workshop: when you activate its ability to become a creature, it does not enter play as a creature, thus not triggering a number of effect depending on a creature/permanent to enter play
Actually Magic needs very very little errata. Clarifictions? Maybe, but I always found that a thorough reading of the Comprehensive Rules gives a remarkable insight into the game.
Clarifications in Magic make me react less "WTF I never would have thought that" and more "Oh, that's right, how silly of me to not get that by myself". M:tG's comprehensive rules manages to keep coherent a game with roughly a thousand new cards printed every year, as such it's like a work of art in the form of a rulebook to me.
Edit: Perhaps this could be discussed as a possible rules change then, as now that I consider it, it does seem more reasonable that they don't enter play just because they became targets, since they were already in play.
Think about it thematically: When Miss Information flips, she becomes a target. Her card was already in play, but it was only when her secret identity is revealed that Expatriette has something to shoot at. If the target did not enter play Hairtrigger Reflexes could not react to her unveiling and Expat would just sit there helplessly while the erstwhile secretary laughed in her face. The same applies to Imbued Vitality. Ongoings are normally just static effects that require massive RPG-style intervention for Expat to handle. When that Reactive Playing she’s been dancing around suddenly comes to life, however, you bet your ass that she can recognize a puny 6hp target when she sees it, and come out with guns blazing.
Was there a target in play before? (No.) Is there a target now? (Yes.) Did a target therefore enter play? (Yes, indeed.)
I can understand a subjective, personal complaint about aesthetic and intuition involving game mechanics such as a target “entering play” when a non-target already in play becomes a target. That is no problem. But I wouldn’t call a consistent, clearly worded rule with an odd corner clarification to be bad design.
I would call it bad conveyance.
Not trying to be difficult, but this is a ruling that seems to be consistent and reasonable if you examine the rules glossary and go with a literal interpretation. It isn’t broken, arbitrary, or prominent in the game.
There are many nuances in the rules that are far less intuitive or clear than this one, and as a rule it’s pretty simple once you get a grip on the terminology.
But a dislike of its aesthetic quality and conveyance? No disagreement here. It could be more obvious and I imagine it will confuse a few playgroups.