The validation pattern UUID module provides needs a little refinement. The current pattern simply checks for hexidecimal numbers, lowercased, in the pattern 8-4-4-4-12. The accepted patterns are a little more nuanced than that.
In the canonical representation, xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx, the most significant bits of N indicates the variant (depending on the variant; one, two, or three bits are used). The variant covered by the UUID specification is indicated by the two most significant bits of N being 1 0 (i.e., the hexadecimal N will always be 8, 9, A, or B).
The variant covered by the UUID specification has five versions. For this variant, the four bits of M indicates the UUID version (i.e., the hexadecimal M will be either 1, 2, 3, 4, or 5).
Additionally, UUIDs are case-insensitive, per RFC4122 Section 3:
'The hexadecimal values "a" through "f" are output as lower case characters and are case insensitive on input'.
More detailed info is available from the RFC4122 document (which I know the maintainers are familiar with; not implying anything).
I'll attach a patch with an updated validation pattern.