1888 H. Sweet (new ed.) 169 Long vowels are regularly shortened in ME before two conss., except..before those cons.-groups which lengthen short vowels.
1924 A. Mawer 6 Blæc, OE, ‘black’, are often very difficult to distinguish owing to the shortening of vowel which the former may undergo in a compound before a consonant-group.
1965 W. S. Allen iii. 68 Complex consonant groups.