It is known from the literature on Squliq Atayal that phonological vowel reduction in the language affects all but the final two vowels. An examination of the Squliq data shows that the weak/reduced vowels appear not only in prepenultimate but also in penultimate syllables. This paper examines the patterns of Squliq vowel reduction in the literature and discusses three more cases where the penultimate syllables of a Squliq word contain a reduced vowel. It is shown that the unexpected weak penultimate vowels as hinted in previous descriptions of vowel reduction do not come from reduction; they are actually related to the historical development of Proto-Atayalic schwas. In two of the three additional types of data identified, the penultimate weak vowels are shown to have occurred in the antepenult at a certain stage followed by the development of the disyllabic suffix -ani to -an (cv.at) or due to coalescence. The one remaining case involves penultimate weak vowels that might be reanalyzed as epenthetic in the synchronic grammar. Although pretonic weak vowels in Squliq exhibit phonetic properties of intrusive vowels, phonologically they come from vowel neutralization, epenthesis, or historical schwa or full vowels that still retain underlying vocalic status in the synchronic phonology of Squliq. The idea of empty vowels is adopted and extended to account for related sets of Squliq data such as infixation.