Why do I get warning L6480W when I use the "Execute-only Code" option?

I'm experimenting with different configuration options, and the "Execute-only Code" option might be useful for my application. However, when I enable it, many modules throw the following linker warning:

Warning: L6480W: Disabling string merging for <foobar>.o(.conststring). Relocated MOVT referring to string .conststring has a non-zero addend, which is not supported.

What does this mean? I notice that the option causes the size of the output hex to increase, so I would guess that this warning just means that the linker isn't able to do some optimization with strings that are used in multiple places in the code, but I'm not sure.

I am using ARM Compiler v5.