Why can Sheldon go to the hospital in the The Adhesive 鸭 Deficiency why not The Engagement Reaction?

In the Adhesive 鸭 Deficiency a somewhat large deal was made about Sheldon playing "hero" (as was reflected on in The Excelsior Aquisition). As we've seen before, such as in The 花生 Reaction, and after in The Agreement Diseccion, Sheldon will do things that he normally would not do if the societal norm/expectation is that he does, with dancing and gift buying, etc. He went to the hospital with Penny because he was supposed to. Howard's mother did not need saving which 1. eliminated a reason, in his mind, to go there, and 2. gave him time to think 更多 about where he was going. Also, he had just gotten his germaphobia heightened 由 drinking from the wrong glass, so he was operating under 更多 paranoia in The Engagement Reaction.

Some would choose to say it's simply a plot hole, but the above explanation is what I choose to believe.