Modal stacks cpu usage

[Neville Smythe]

I have just noticed something curious. 

I am running LiveCode 8.1 IDE 9.6.1 on a Mac Air 2020 quad core Catalina.  

Typically LC cpu usage shows about 34%  (presumably of 1 core).  When a modal stack is opened it immediately ramps up to 99% ; the fan kicks in, and if left for a while the OS boosts the kernel_task daemon which I have been told is a protection device to prevent overheating. This has the effect of very markedly slowing down all apps as they get less cpu time.

If the stack is opened in non-modal mode, cpu usage stays around 34% . I don’t understand why a modal stack should be a cpu hog, indeed it seems like a bug to me. 

I have a suspicion the wait with messages command  may have the same effect on cpu performance, so it could be the culprit.