I keep on finding exceptions that doesn't fit into the rule that a grammar book suggests. One of them is about changing regular verbs to past simple. It says, if the verb ends in a vowel + a consonant, you double the consonant and add -ed. i.g. stop > stopped, plan > planned, mop > mopped.
However, I found 'play' also ends in a vowel + a consonant, still it doesn't double the consonant. Same as 'slow' and 'screw'. I recently learned about syllables, and 'y' at the end of word is considered to be a vowel too, not as a consonant. I wonder if these are the similar cases.