After splitting a phrase that is a heading, the second part of the phrase can't be reassigned as heading

[chhavi-negi]

Steps:

1. Open any project and assign a phrase in it as heading.
   
2. Start playing this phrase.
   
3. At a random postion anywhere between playing split the phrase by Ctrl+Q.
   
4. Now click on the second part of the split phrase which is a plain phrase.
   
5. Right click on it to assign it a role, and we see that heading role is hidden or disabled.

[avneesh-singh]

There can be only one heading phrase in a section. So you need to clear role of the first phrase which is marked as heading and then assign this phrase as heading.