Looking at transparent blocks in an item frame allows you to see through some blocks.
In the screenshots shown below, you can see through the chests of which have stained glass in the item frame. I have not seen what other blocks are affected.
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violine1101
Thank you for your report!
We're actually already tracking this issue in MC-162042, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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