Long string not ended by EndPreamble

[lorenzobertini97 at gmail.com]

Dear list,
since at least a year I've been getting the following after validating
a local layout in document preferences:

> LyX: Long string not ended by `EndPreamble' [around line 4 of file 
> current token: 'EndPreamble' context: '']

It happens with Preamble, AddToPreamble, HTMLPreamble,
AddToHTMLPreamble even when closed by EndPreamble. Can someone
reproduce?

All the best
-- 
Lorenzo