Past tense sentence containing a habitual action in present tense

Solution 1:

The answer to this query is found in A comprehensive grammar of the English language.

(CoGEL § 19.42) Special Uses of present and past

[…] the present tense can cooccur in textual structures with two distinct types of time references: ordinary 'state present' and universal 'state present' (timeless)

♦ I think she had undergone an operation before I met her. [ordinary]
♦ Troilus is totally fancy-free until he sees Creyside. [timeless]

A third type of present, 'habitual', is common in ordinary narrative, and it can really cooccur with past tenses:

♦ I had forgotten that they dine very early and I arrived at an awkward moment for both them and me.

He must have known that I always walk my dog in that park. Why else would he have been there?

She knew that I don't answer the door after 8 pm, so she rang me instead.

She knew I never use Skype. That's why she came over to my desk to tell me the news.

I thought you knew I don't drink?

In all four sentences, the type of present used is the habitual present, (I am in the habit of walking my dog…/of not answering the door…/of never using Skype…/of not drinking); therefore there is no problem in using it with the past perfect and the past simple, as this is done in the sentences; it follows that there is no error in those sentences. Here is another instance , that of a sentence in which is found the past perfect.

• If she had known I spend Sunday mornings fishing by the pond, she would have found me.