Strange variable manipulation failure?

[Fairlight]

Question:

I was helping someone debug a problem in fP.  They were doing processing
and simply getting the mid() of one variable and storing it in the same
variable.  I've done this day in and day out for years in many languages,
including filePro when I code in it.

Problem was, they'd have something like:

:'some condition:long_name = mid(long_name,"4","16"):

Now apparently, what we narrowed this down to is that following that line
testing true, long_name would be empty, rather than contain the contents of
the mid().  However, at the same point in time in the debugger, the mid()
expression would yield the correct data.

I asked them to humour me and put a middle variable in there:

:'some condition:aa=mid(long_name,"4","16");long_name=aa:

This gave them the expected results--IOW, it worked fine.

But stranger yet, the following works:

:'some condition;aa=mid(aa,"4","16"):

It -seems- like you can't re-store the contents of a declared variable
from inline from the mid() function.  This was the case on both 4.8.10 and
5.0.14.  You can apparently do it to a dummy, but not a declared long.

Anyone else run into something similar?  I find it puzzling.  Known
issue/feature with a rationale, or bug?  I'd think the rvalue would get
evaluated first and the results stored in the lvalue variable last in any
event, but from all appearances the variable types were treated differently.

mark->
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