what is a type-E constant in the OPM dictionary?

What is the difference between type X'6' and type X'E' constants in the OPM
template?

Today I was emailed an observable program to disassemble for MI, and one of
the ODT entries begins with nibble x'E'.  What does it mean?  The GENOPT
(*LIST) documentation for ODT entries states the first nibble means:

x'0' = scalar
x'1' = pointer
x'2' = entry point
x'3' = branch point
x'4' = instruction definition list
x'5' = operand list
x'6' = constant
x'7' = exception monitor
x'8' = machine space pointer
x'9' = unsigned binary
x'F' = OES offset exceeds 64K-1, so look in OES for real type

but x'E' never occurs.  The emailed program was not generated through
QPRROOTP, but through something else.  The context where this emailed
program used the type-E thing showed the thing to be some type of right
hand side constant with intial value string in OES, for example:

CPYBLA, STRING, "hello word";

Now what was so different about this string that it took a new ODT entry
type x'E' instead of the regular x'6' ?