In 5.2pl0, multiple legends land on top of each other after the "at end" option is used in one plot
plot -x, for [i=1:5] i+x title "i=".i at end, -2*x
That's a regression from 5.0pl6.
Additional question: Can I switch off the legend for the plot that used "at end", but not switch off the legend completely?
The "title at {beg|end|<position>}" options were conceived as an alternative to using the normal key, so mixed use with some titles inside the key and others outside was not tested. You have a good point that it should be possible to move a title out of the key without messing up the key layout.
Partially fixed in CVS for 5.2 and 5.3
This isn't a complete fix, however, because it interferes with toggling plots on/off by clicking on their key entry. It's not clear what to do about that. In that respect the behaviour in 5.0 was better.