While playing through a combat, I noticed that an enemy ship was not closing on my own at the expected rate.

I investigated, gathered the details, and began typing up a bug report:

Distance traveled over time does not reconcile with movement speed.

Situation:
My missile escort and an enemy contact are moving directly towards each other.
My escort speed is 1493 km/s.
Enemy contact speed is 5377 km/s.
Net expected closing speed is therefore 1493+5377 = 6870 km/s.
Net expected range reduction per 5s increment is 6870 * 5 = 34350km.

At 09:55:15, I launched AMM missiles at the contact. The Events window reported the range as 6,051,747km.
At 09:55:20, I launched ASM missiles at the contact. The Events window reported the range as 6,032,327km.

Those range reports indicate a net range reduction of 19420km in 5s.
This does not match the expected range reduction of 34350km.
(The reported speed of the enemy contact has not changed, either just prior to firing or during the single intervening increment.)

The reported range reduction implies a net closing speed of 19420/5 = 3884km/s (about 55% of expected).

Fast forward to missile impact.
My AMMs have a speed of 14600km/s.
My ASMs have a speed of 14595km/s.

At 10:00:20, the AMMs arrive on target.
That's an elapsed time of 305 seconds, for a calculated distance of 14600 km/s * 305s = 4453000km = 4.453mkm

At 10:00:25, the ASMs arrive on target.
That's an elapsed time of 305 seconds, for a calculated distance of 14595 km/s * 305s = 4451475km = 4.451mkm

At the time of ASM arrival, my escort's fire controls showed a range of 4.85mkm.
This range reduction over 305 seconds also implies a net closing speed of 3884km/s.
It seems as if

And that's when I realized what was going on.
My missile escort move command was not "Move To Location", it was "Follow" (at 6.5mkm distance).

The actual net closing speed was not the sum of the two fleet speeds, it was the enemy's speed minus my escort's speed.
5377-1493 = 3884.

In other words, this turned out not to be a weird bug, but a straightforward PICNIC.

Oh I see, in the RIGHT hand list! It never occurred to me to test multi-detach from there, thanks!

Yes, the tree view is a Microsoft control and it doesn't allow multi-select.

In the Environment tab, together with the Annual Terraform capacity, I would like to read the number of the Terraforming Istallations active on (or near) a body.

Added for v2.6.

It's basic, but I admit I don't know if there is a solution. Is it possible to move several ships at once from one fleet to another? Ctrl-click does not work for multi-selection, but I can't imagine that after all these years Steve is still moving 36 fighters, one click at a time, from one fleet to another (fighters, FACs, or whatever; you get the idea!).

In the Environment tab, together with the Annual Terraform capacity, I would like to read the number of the Terraforming Istallations active on (or near) a body.