What was the strange thing that inventor noticed as they were trying to improve the telegraph?

Signals were going through the air to other wires.

Inventors noticed amongst other things, that the telegraph as invented by Samuel Morse could not transmit non-English texts because of the absence of letters with diacritical marks. It was also discovered that the Morse code could not send/transmit signals in two different directions on the same wire.

Explanation:

A telegraph is an instrument or device that is used to send messages or communicate between people with the use of electric impulse or coded signals. The electric version of the device was invented by Samuel Morse in the 1830s. In improving the device, inventors like Thomas Edison noticed that the Morse code used for the traditional telegraph could not transmit signals across two different directions on the same wire, so he invented the quadruplex telegraph which was capable of sending signal along different directions on the same wire.