Templates and transposed instruments
Open a template with transposed instruments, for example the Concert Band template, directly in Musescore.
You will see that all the transposed instruments are correct. Close it again.
Now start "creating a new score from template". You chose the concert band template. You are asked for a key signature. Chose one. result: all instruments are in the chosen (concert)key.
Here is what it should be: The key you chose should be the concert key, but all the transposed instruments should transpose to the correct corresponding key.