Originally Posted by Brian Carlton

Here is a postulation of a possible outcome that is not in agreement with your conclusion:

The one variable for which you are ignoring is time. A fuse does not melt instantly upon application of the rated current load, or a load that is slightly above the rated current. The fuse must gradually heat to the point where it will melt the alloy. This will always occur directly in the middle of the fuse, because the edges of the fuse are, effectively, a heat sink.

When one solders the fuse in the middle, the remaining strip will be closer to the heat sink, and, therefore will melt somewhat later than the original fuse with the same current applied.

Note that the assumption is that the solder joint melts at a higher temperature than the strip fuse. If incorrect, the entire discussion becomes moot.

Note, additionally, that the delay in the time for melting of the remaining strip is probably insignificant with regard to the protection required for the device, however, it is noted to correct your conclusion of "inexplicable".