Meaning of ～ことは～ようか

Question

In an anime I heard the line

戻ることは戻ろうか。中のほうが暖かいし

which was translated as "But we probably should head back. It's warmer inside". I know the ～ことは～ようが form, meaning "but" (like 「この薬は効くことは効くが、飲むと眠くなってしまう」), but I wasn't able to find the form with ようか, so I was wondering what's different: the AようがB form means "A, but B", while from that anime line AようかB seems to mean something like "But we should A, [since] B", but without having more examples it's just a wild guess.

Edit: The protagonists went outside to try a boomerang one of them gifted to the other; after trying it for a bit, one of them says the sentence I'm asking about, and starts heading inside.

Here I uploaded the audio, if anyone wants to check if I heard correctly.

Edit: more context: Adachi met Shimamura for the first time not long ago and they became friend; she's clearly in love with her, while at the moment Shimamura's feelings aren't so clear.

They spent Christmas together, then exchanged gifts: Adachi got a boomerang, so they head outside to try it. She isn't able to throw it very well (Shimamura's comment is いまいち), though she does some nice tries not having used one before, so Shimamura asks if she should buy something else and Adachi says she likes it. Then Shimamura acknowledges this (そう) and says the sentences I asked about.

Answer 1

Actually there is no difference between your two examples (戻ることは戻る and 効くことは効く). This pattern is used when the speaker reluctantly admits this action, but wants to imply it is associated with something undesirable at the same time.

Note that the "undesirable" part may not be explicitly mentioned. In other words, this construction is usually used with が/けど, but that's not a requirement at all:

• この薬は効くことは効く。
  この薬は効くには効く。
  This drug is "effective", at least.
  Well, this medicine does "work".
• 中の方が暖かいので戻ることは戻ろう。
  中の方が暖かいし、戻るには戻ろうか。
  It's warm inside so let's head back (although ...).
  We should head back at least cuz it's warm inside (but ...).

So 戻ることは戻ろうか means she has some other concern, but convinced herself to go inside anyway. For example, she may have wanted to stay outside because she was waiting for someone. Please check the context again.

A similar pattern exists with nouns and adjectives.

• 彼はいい人はいい人ですよ。
  Well, I admit he is a "nice" person (but...).
• まあ美味しいは美味しい。
  It is good in terms of taste (but...).

These imply there is something bad at the same time without explicitly saying が/でも.

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EDIT: I checked the video. The actual conversations is as follows:

S「イマイチ？」
A「うーん……。」
S「そっか……。あ、今から戻って何か別のを買おうか？」
A「いい、いい。気に入ってるし。」
S「そう。でも、戻ることは戻ろうか。中の方があったかいし。」

So this 戻ることは戻ろう means not "Let's get back anyway (although I want to stay)" but "Let's get back anyway (although we won't buy a new present)". Shimamura suggested 戻って and 何か別のを買おう, and Adachi said they don't have to, implying they can stay longer. Still, Shimamura read between the lines and said "At least, let's get back." After all, this type of は is the familiar contrastive-wa used when there is a contrast.

Answer 2

In this context 戻ろうか means something like I want to (I thinking about) head back, how about you? or I want to head back but not sure, what do you think about it?. It pretty close to 戻ることは戻りますか, but 戻ろうか is using when we want to get some advice or acceptance. 戻るか (or 戻りますか) is own opinion/decision. I decided to head back, what about you?

Here is good explanation in Japanese.

I don't think that you should translate ～ことは～ようか as a monolithic construction. (But not sure about it)

Actually AことはBが、Cです may be splitted on three sub constructions:

Aことは → what about A B → action / meaning / explanation C → negative addition / disagreement

So

AことはBが、Cです → What (I think) about A, that is B, but C

この薬は効くことは効くが、飲むと眠い == この薬は、効くのは効くが、飲むと眠い == この薬は効くが、飲むと眠い ← same meaning

And I checked from Japanese friend,
He said that 戻ることは戻ろうか sounds strange. And he is don't understand meaning without context.