Converting bit-depth resets LUTs

Hello,

I've noticed that in v1.53h, if I change the bit-depth of an image the LUTs can also change.

The following macro shows the issue; magenta becomes red if `run("8-bit")` is called, but not if it is omitted.
```
run("HeLa Cells (48-bit RGB)");
run("Magenta");
run("Duplicate...", "duplicate");
run("8-bit");
```

The following works as I expected in 1.51w:
```
run("HeLa Cells (1.3M, 48-bit RGB)");
run("Magenta");
run("Duplicate...", "duplicate");
run("8-bit");
```

Is this a small regression, or is it intended?

Start by running the reported macro with the HeLa Cells images and compare the behavior of run("Magenta"), Duplicate..., and run("8-bit") in the two versions mentioned. Trace the 8-bit conversion and LUT handling to determine whether the LUT change is a regression; done means conversion preserves the LUT behavior expected by the report.

Written by the indexing model from the issue text.