If you place down a light block at any light level and interact with it to increase the light level you will see a jumbled mixture of numbers for the light level until around 10 seconds later it shows the correct number. When you change the light level from a low number to a high number the issue becomes more apparent as you do not know what light level you have it set as.
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We're tracking this issue in MC-47660, so this ticket is being resolved and linked as a duplicate.
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