Thank you for save. I'm a bit slow today, as I just realised what this one is - it's actually an intentional change affecting only the tooltip.
https://github.com/Interkarma/daggerfal ... 541f335c69
This was done for performance and stability reasons. Expanding quest macros can involve loading world cells to organise information, which can cause significant problems in inventory, especially in modded games, for the sake of a tooltip text. It does not affect the actual letter contents.
Edit: I've made a change now to only display the final line of letter in tooltip, not the final two lines. I think this looks better most of the time as it only has the actual sign-off for most letters instead of partial text from letter itself. So you just need to ensure final line of letters doesn't contain any macros. This change will be in 0.16.3 or 1.0, whichever comes first.