When I placed a sea lantern on the surface, but in, water, the light got cut off (Placed Sea Lantern pic). After breaking it, the light was still there but changed (Broken Sea Lantern pic). I placed more, and it only worked sometimes, and I was able to light up most of the water I placed (More Sea Lanterns). I also included a screenshot taken before placing any sea lanterns.
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Can confirm. Happened in my world as well.

Should maybe mark it as related to MC-128299

Fixed in 1.13-pre4.