Bug check, undockable debris has power.

[boolybooly]

I found that a complex part (solar array extension) became undockable when detached.

It had no control pod but did have 2 jr docking ports matching the docking vehicle and a fully charged battery but no active solar panels and it failed to engage when approached even after game reload. You could switch to the part and it showed a full battery.

Is this as intended ? It means you cannot detach parts and go get them later.

[Padishar]

Not sure if it is intended, I can't say I've ever tried it myself, but there is a long-standing bug where docking ports fail to engage because they get stuck in the wrong state.

See this thread for details and a way of unsticking the port if this is the problem.