The answer is essentially yes.
but bad blood already lor... if I am the employee, i will start to think whether it is time to consider somewhere else.

but of course best to talk it through with the supervisor and see if the super can rearrange or readjust to come into a acceptable compromise.

for manpower planning...

but unexpected biz issues can happen, and the priority is the firm's ongoing biz.

a good firm and manager will try to avoid sudden cancellation of leaves, but the firm's priority is towards the ongoing biz.

the firm should, but I don't think it is required to do so... unfortunately...