Midline of a fraction

Under what circumstances does the midline of a fraction become left-shifted? The presentation markup used here is not always fully elaborated. For example, sometimes InvisibleTimes is omitted.

Here we have

$$\frac{a}{b}\frac{c}{d}=\frac{a}{d}\frac{c}{b}\text{.}$$

Here is the same after removal of the two InvisibleTimes operators joining the two pairs of fractions: $$\frac{a}{b}\frac{c}{d}=\frac{a}{d}\frac{c}{b}\text{.}$$

Here is the original after removal of the third mrow wrapper: $$\frac{a}{b}\frac{c}{d}=\frac{a}{d}\frac{c}{b}\text{.}$$

Here is the original after removal of the second mrow wrapper: $$\frac{a}{b}\frac{c}{d}=\frac{a}{d}\frac{c}{b}\text{.}$$

Here is the original after removal of the first mrow wrapper: $$\frac{a}{b}\frac{c}{d}=\frac{a}{d}\frac{c}{b}\text{.}$$

Here is the original after removal of both of the first two mrow wrappers: $$\frac{a}{b}\frac{c}{d}=\frac{a}{d}\frac{c}{b}\text{.}$$

Here is the product of four fractions without any mrow wrapping.

$$\frac{a}{b}\frac{c}{d}\frac{e}{f}\frac{g}{h}$$

A product expression displayed by itself:

$$\frac{2}{3}\left(5\right)$$

Again reversed. $$\left(5\right)\frac{2}{3}$$

That way with an explicit first-level mrow. $$\left(5\right)\frac{2}{3}$$

In the denominator of a fraction $$\frac{1}{\left(5\right)\frac{2}{3}}$$

The same product expression is simplified.

$$\frac{2}{3}\left(5\right)=\frac{10}{3}$$

The same after removal of the mrow wrapper. $$\frac{2}{3}\left(5\right)=\frac{10}{3}$$

Again reversed. $$\frac{10}{3}=\left(5\right)\frac{2}{3}$$

The last revised using first-level mrow wrappers.

$$\frac{2}{3}\left(5\right)=2\frac{5}{3}$$

The last after removal of the second mrow wrapper: $$\frac{2}{3}\left(5\right)=2\frac{5}{3}$$

After removal instead of the first mrow wrapper: $$\frac{2}{3}\left(5\right)=2\frac{5}{3}$$

Or when the last fraction is mfenced: $$\frac{2}{3}\left(5\right)=2\left(\frac{5}{3}\right)$$

Or when the last fraction is surrounded with "(" and ")" as mo's. $$\frac{2}{3}\left(5\right)=2\left(\frac{5}{3}\right)$$

And the last with no explicit mrow's at all. $$\frac{2}{3}\left(5\right)=2\left(\frac{5}{3}\right)$$

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